I think slash pertains to any non-canon m/m pairings, regardless of their sexuality in the canon itself.

Chan? I've only heard it called shota...never chan, but I am really into yaoi/manga lately, so I must have missed that. Terminology aside, I'm not a fan of underage sex, unless both parties are underaged...and even then, I don't like them to be TOO young. To me, rape fic is a huge squick, too.