If your friends refer to you as he/him, and you are happy with that, then those are your pronouns. E.g., "this is my friend so-and-so, he went to x college, but you being a y fan won't bug him" would be someone using he/him pronouns for you.
Mine are he/him. I don't bother telling people this on profiles, but I am cis and male-presenting, so people meeting me irl always guess my pronouns right.
On introductions: one totally cool option is to suggest introductions, start with introducing yourself and add your pronouns. This will alert others that you are gender-conscious, which will be welcome by queer and queer-friendly people.
Don't fret over it, in the same way you wouldn't fret about whether someone is a vegetarian or not. "Would you like some nuggets?" "Oh I'm vegetarian but thanks" "oh ok cool, I'll remember in the future."
Likewise, "hey did you like his idea?" "Oh actually I'm a they/them" "oh ok, I'll remember in the future."