I don't know if it's generational (being 32 here), but fullstops in realtime conversations (email is different) always seemed used to highlight annoyance or mil

I don't know if it's generational (being 32 here), but fullstops in realtime conversations (email is different) always seemed used to highlight annoyance or mild anger indeed (perhaps because it emphasizes that you want to end conversation). It's similar to replying "k" (or a single word) to someone who sends you a full sentence.