A really, really ugly guy. Usually a one that hits on you or in some other way shows an intrest in you. The actual definition comes from the cold hard truth the guy's face resembles a dog's butt or is infact uglier than one. Either that, or his personality totally blows.
"Ugh. Why do I always get all the dogs butts?" Emmy cried after Tom the pizza faced Sophmore with the permanent allergies gave her a cafeteria cookie and a hand drawn stick figure portrait. "It's like I'm a dog butt magnet of something."