Most Helpful Guy
Look at the other end, what isn't slutty? Completely covered, but that's completely conservative.
Work backwards from that, and you have some average - clothes that fit and only show extremities.
Start going further than that and you start becoming provacative in how you dress, showing off more of the torso - midriff and shoulders - and more leg - upper thighs. These are more erogenous areas and are associated with sexual ideas.
That last part is very subjective, so to really make something declarative, if I see more than, about a third, of a girl's cleavage, she's trying to show off. If I can see her ass falling out of her shorts, then she's trying to show off. If she is in anything skin tight, and there isn't anything over it, she's trying to show off.
In any of the above case, it shows a part of the personality of a slut and would be considered slutty.
Are those outfits slutty? The first girl is pretty much wearing just a bra. Second is better but not by much, it's just a shirt. Third has a transparent top and really shows off her skin, but she could also cover up with the jacket. Fourth has just a bra and Daisy Dukes on, and is really showing herself off.
Talk to normal girls who don't go out to get laid every other night, they'll say these girls aren't wearing a lot either.
Most Helpful Girl
I don't really find any of them slutty... as long as they're in the appropriate place like a park or beach - not at school or work.
When I think of trashy clothes though I think of