I don't think anyone would ask, since no one really cares what I do on the Internet in my home. However, if someone asked, I'd be proud to announce I'm part of a Pokémon forum, because, well...it's so much more than that.
The PokéCommunity is a place where you can meet new people, make new friends, get life-changing advice, ask for help about pretty much anything, post your art and have people give critics and opinions, talk about today's most popular topics, get news about what's going on in the world, get into big arguments for no reason, and finally: talk about Pokémon. I don't think anyone out there could possibly understand how great we are as a whole, instead of just looking at the title and thinking it's for ten-year-olds.
I'm going to be a sophomore this year, but heck yea I'll announce proudly that I am a member of PC and visit daily! You're never too old for having fun in my opinion, and that's what this place is about, no? Just having fun. Nothing to be ashamed of here.
I bet if you checked your friend's Internet history, they'd be a lot more ashamed of that than you are about PC...