Thanks for this reply; it appears you spent a lot of time on it, and I appreciate it. I agree with some of your points and most of your examples, but on certain points my interpretations are different; I'll try to reply to your arguments and explain what I think.
1. Race. I agree that to a large extent, "race" is defined and interpreted by humans, and there is no clear biological distinction, and whatever categories we try define are very fuzzy, overlapping and changing. However, in my view there is a clearly obvious biological fact that there are distinct races, e.g. white, black, Asian [1] [2]. Sure, the categories are somewhat arbitrary and were made up largely to group large numbers of similar people together, but I nevertheless find the concept of race useful. For example, it can be used as a description ("the black man" if there is one black and one white person), or to make certain assumptions (e.g. in Slovenia, a black or Asian person is almost invariable a foreigner, so I'd use English to address them). Also, I agree that the concept itself is a bit controversial, both because there are more and more people of mixed race, and that people use race to make useless, harmful distinctions (e.g. "black people are criminals", or "whites with dreads are appropriating black culture", or "my skin is white but I identify as black" as I mentioned before).
[1] http://econintersect.com/images/2014/11/15608366ztemp.png http://econintersect.com/images/2014/11/15608366ztemp.png
[2] http://shirleymaya.com/wp-content/uploads/2013/12/Beauty1.jpg http://shirleymaya.com/wp-content/uploads/2013/12/Beauty1.jp...
2. Geek. I don't see "geek" as my identity, but merely as a description; the description, of course, could instead be elaborated into "likes computers, dislikes group sports, introverted" and so on, but given that there are so many people that share this attributes that they even form groups and share common experiences and culture, a description such as "geek" is useful. In contrast, if someone is using "geek" just as an identity (i.e. "I don't like computers, I like sports, and I'm really extroverted, but I'm still a geek") without otherwise fitting the description, I find that pretentious and fake and hence I dislike it.
Note that not everyone might agree with above description of what constitutes a "geek" - even I could list many more attributes and I agree that not every geek fits all of them; but it's the same way with many other terms that nevertheless have broad, common usage, e.g. "object-oriented programming" [3] ; and they're still useful, in the sense that most people would agree with "C is less OO than Java, which is less OO than Python".
Temporally, I'm not particularly attached to the word "geek". In particular, if my preferences ever change, I'll gladly admit that I no longer fit the stereotype of a "geek" and adopt a different fitting description shortcut. Admittedly, I'm probably less of a geek now then I used to be, because I've tried to be less introverted (not necessarily because it's my preference, but because I find it useful in achieving other goals); I still like math though :) Also, I'm perfectly happy if the word "geek" was used in a different way in the past (c.f. "gay"), or if it ever changes in the future. I would object a forceful redefinition of the word, such as what some people are attempting to do with "man"/"woman", because I perceive that as a political statement, indicative of a sort of "holier-than-thou" belief. Then again, my opposition to the redefinition of words is just as much of a political statement ("leave me alone and let me be") as others' attempts to redefine the words ("we're better" than you and our world is more ideal* than yours"). Pluto will always be a planet for me.
Also, I don't really care if I'm a geek because I was born that way, because I was intentionally raised that way, or because of some other non-genetic influences. Of course a lot of my preferences exist because of familiarity; but at the same time, I'm pretty open to trying new things, in fact I'm drawn to it. (More on this later...)
[3] http://www.paulgraham.com/reesoo.html http://www.paulgraham.com/reesoo.html
3. Pride. You can totally be proud of actions of other people, e.g. your father or your ancestors. But I don't think that you're justified about feeling better about yourself just because your ancestors are great; equally, I don't see a reason you should feel bad because your ancestors were shitty (e.g. "white guilt" [4] (especially when wielded as insult against white people that never enslaved, colonized or otherwise oppressed any other group of people, and were actually oppressed themselves, e.g. most Eastern European Slavic nations), or the idea that Germans should feel bad for what their ancestors did).
[4] https://en.wikipedia.org/wiki/White_guilt https://en.wikipedia.org/wiki/White_guilt
4. Identity. Most examples that you list I would classify as "description" or "preference" rather than "identity". I'll address the following ones: Muslim, manager, nurse, and male/female (regarding clothing and behavior).
I understand "because I'm a manager" as purely descriptive; s/he's just using the implied general knowledge about cultural/social standards about how managers (and the like) are expected to dress in most companies. Indeed, saying "because I'm a manager, and managers are required to wear suits" would be superfluous. There's also the social status that comes with being a manager that might be the reason someone mentions it. For example, a friend of mine has a graduated response to the question "what do you do"; he can answer either "I work in finance", "I work in a hedge fund" or "I'm a trader", depending on how much he wants the audience to know (or not know) about his income and/or wealth.
It's similar with a nurse; if someone said "I like being a nurse", I would understand this as an expression of preference, in the sense of "I like most things that come with the job of being a nurse" (e.g. caring people).
I'd say that being a Muslim is the most identity-like. In the strict sense, "Muslim" means "someone who believes in and lives according to Quran", so someone saying "I'm fasting because I'm a Muslim" would mean "I'm fasting because my preference is to follow the Quran and Quran says that I should fast during Ramadan." In a broader sense, "Muslim" is also a culture, so you might want to observe certain parts of the culture even though you don't believe in Allah.
A better example: "Jewish" is denotes a religion, a culture, and an ethnicity. So if someone says "he's a Jew", that might mean a biological fact ("he has a Jewish mother"), or a preference ("he likes living according to Jewish religion/culture"). Furthermore, people will pick and choose different traditions for different reasons; some eat Kosher, others only avoid pork, yet others eat everything; some are Orthodox, some insist on marrying Jews because that's what their parents expect of them, some just don't care. People do strongly identify with being a Jew, so it is an identity of sorts, but in the end, it's largely a voluntary choice.
The most obvious example where "Muslim" is used as a description is the finer distinction between "Sunni" and "Shia" Muslims; sometimes, they present a united front (e.g. when protesting depictions of Muhammad), at other occasions, they slaughter each other (now in Syria). We don't have any shortcut word for the description of "people who perform circumcision", but both Jews and Muslims fall under this description, and they present a unified front when necessary (e.g. when protesting the German decision to ban circumcision).
Finally, regarding male/female, masculine/feminine. Mostly as I said above, I consider these mostly descriptive. For example, I sexually I prefer women (because I like touching pussy, but not other dicks), but I prefer girls that "think like a man" - more analytically, less emotionally (IME men are more likely to be like that). So I totally don't get why "tomboy" would be considered an insult; my answer to the Quora question would be "you probably have no reason to feel bad about it!" On the other hand, I'm visually attracted to attributes that are stereotypically feminine: long hair, full lips, boobs.
I dress like a man (1) because I was brought up that way, so I'm used to it and it's very convenient for me, and (2) because it's useful - not necessarily useful just in ways you mentioned, but mainly socially useful - I'm aware of the fact that if I wore girly clothes, people would perceive me differently. Now, you might say it's bad and we're working on changing that perception, but in the area that matters most to many people - intersexual relationships - there's barely any change. Women still crave masculine men (even feminists [5]), while men still crave feminine women (in general; there are exceptions, of course). You can see that even in same-sex relationships - often one partner will be more masculine and the other more feminine! I don't otherwise have no attachment to the specifically masculine way of dressing, and sometimes I envy women their broader range of socially-accepted clothing.
[5] http://www.people.com/people/article/0,,20774276,00.html http://www.people.com/people/article/0,,20774276,00.html