Also, just on the side topic, it's pretty much impossible to dress up as a female superhero and FAIL to look slutty. If we are going to be honest most female costumes are either full body suits that are more than skin tight, or they contain less material than sub mariners trunks!
There is levels of sluttiness. Rouge, while skin tight, is fairly covered (people tend to wear the green/yellow costume), while the Emma Frost as the White Queen is well....you know.
And I am not saying the sluttiness is a problem, its one of the categories of Cos fans you see at a convention. Its usually either one of the Big names, way super obscure, or slutty.
Only real problem with slutty costumes is about 50% of the time, the person who chose to wear said slutty costume misjudged their ability to pull it off quite remarkably.