How short is too short?

Soo ... We all see it; the group of teenage girls walking around the mall in short-shorts. But, at what length do you stop and think "Wow, that's very revealing." or "Hmph. She looks slutty." Being a teenage girl myself, I'm always conscious if people will think my shorts are too short. ("If you have to question them, then they are." Yeah, yeah, yeah. Lemme finish, please.) I don't dress sluttly, my shorts are paired with tee-shirts and sometimes a tank top/cami, but, they don't reveal anything up top at all. Do you think it depends on the person who's wearing them or are short-shorts are just slutty all around? What if everything is completely covered, even when bent down? Your opinion is appreciated! :)