Wiggling to pull your pants back up?

Because they're tight of course haha.
And even after we have them on, we have to kind of stretch them so they fit comfortably lol. :p

dont want no ass crack showing

It gets them up right and in position. Our clothes tend to be tighter on us, and our seams are a little different. So we get our pants on a little differently.

It helps them go on easier. It just works them up some how. For instance, get 2 paper towel tubes and try to put one inside the other. What's going to end up happening is you will have to bend one slightly and then try to jiggle it on inside the other. Same idea.

its because we like tight pants so that's how we have to put them on

Most girls prefer looking 'cool' to looking 'sensible.' Of course some guys with their sagging pants looked even worse, but it really is funny to watch these girls, no?

But if you say a word to them about how this looks they will be your enemies for life, so let's just keep the joke to ourselves.

The pants many women wear are extremely small, often times they wear pant sizes that are smaller than they should be wearing, so, wiggling helps pull them up.