Do you see boobs/muscles/bulges? Yes, okay, that's tight. Are they really busting out, and are there cleavage openings showing them bust out? Okay, that's extra tight. Of course there's still a subjective component, but it's a lot easier to judge tightness of clothing as one of several factors than simply saying "suggestiveness". A robe is obviously less tight than a chainmail bikini or fitted booby armor...