Why do modern teenage boys sag their pants deliberately?

I sag to show off my designer underwear to my mates and girlfriend. I also tend to get a real excitement out of sagging my pants, as if I'm doing something which is daring and I know I shouldn't really do, but it feels great to show people more than usual. Sometimes I go as far as sagging below my dick and display my bulge. I get a lot of attention when I do that.