Honestly, birthday parties are so incredibly fraught with potential issues they should really not be "celebrated" in the office on an individual level. You have

Honestly, birthday parties are so incredibly fraught with potential issues they should really not be "celebrated" in the office on an individual level. You have all sorts of people who'd really rather not - not just people with anxiety issues, but also religious prohibitions (Jehovah's Witness), and just personal preference. Some people don't like it when others even know their birthday.