A girl/boy who is in their teenaged years who is popular for smoking, drinking, drugs and having many sexual relations. Sloppy and always getting into something they probably shouldn't be. Also tend to use people for money and may come off as rude, bitchy and/or whore-ish, but are often used for easy sex. Involed with friends that are a lot like themselves. Very dangerous to trust, and easy to point out. They're the kids your mom warned you about.
Sam: Are you sure you wanna go to that party? There's gunna be nothing but Dellies everywhere.
Zac: Oh yeah man! I heard that one hirl Kim is a horny Delly and wants to get in my pants.
Sam: Oh shoot! Really I heard that Delly girl has STD's though and is slow from all the drugs though.