Depends what you mean "in public". If I'm in a public area with friends I know, then sometimes I'll swear, but never in vain. If I'm with strangers or people I know less, then I wouldn't swear.
I swear. I just might tone it down a little in front of coaches, teachers, parents. Sometimes that changes though. If something goes wrong with sport I'll swear... Heck, I don't really tone it down in front of teachers either.