(((((((((muse))))))))))))
I've got friends like that, they find it amusing to joke about SI - especially my one friend who KNOWS about mine! It sucks
Depends on the kind of cut/length/depth but one of those bandages that cover large areas? You could say you got a gash from something or other. Normally I don't advocate lying, but I know highschool is rough. University is a bit better for me, nobody cares! (If that's any consolation)
You can get sweat/water proof makeup if you look hard enough. IDK, say you're self-concious about a birth mark or something. People are self-concious about all sorts of things.
I hope you come to some sort of good conclusion.