DDM or D.D.M. is an abbreviation for Designated Drunk Molester. He's that creepy guy hanging around at a party looking to take advantage of the drunkest girl(s) there. They often sip their drinks slowly, yet pretend to be really drunk in order to have an excuse for their actions the next day.
Friend 1 "Did you see Chris at the party last night?"
Friend 2 "Not really; why, what happened?"
Friend 1 "I think he fucked Lauren in the basement"
Friend 2 "She was wasted! I heard she was puking at like 10 o'clock; what time did this go down?"
Friend 1 "11 maybe 11:30"
Friend 2 "DDM strikes again, huh?!"
Friend 1 "Yeah! What a scumbag!"