When I was younger (from, what? 12 to 15/16?), I used to keep it secret. Now I don't care anymore. Actually, I'm proud of my Pokemania! =D
Anyway, when I was in 5th grade (16~17 yrs old [yeah, school systems are different everywhere, so...]), there were some elementary school students (so, 10~11) that somehow learned that I liked Pokemon (don't ask me how...), and they started to make fun of me, calling me "baby", "Pikachu" etc
Everyday they waited for me, and everyday they did that. What they didn't know, though, is that my friend and I stopped near their spot and just wait there and listen to them to laugh beteween ourselves at their stupidity XD
That was cool.
But something that I loved when I went to Japan, is how students openly talked about it during class etc or even played in the streets. I mean, they were at least 17, but no one made fun of them for that. And girls like to draw Pikachu on blackboards =D
I love Japan!