Noun: A giant douche-bag that enjoys posting feed after feed about his awesome life you wish you had. May possibly be, but not limited to, an over-muscular guy that has girls hanging off his eight pack who goes to every awesome party you weren't invited to, or an event you wish happened to you.
Daniel: Man, did you see Tim's post about hooking up with the hottest chick at that frat party?
John: Yeah! He also posted about that massive inheritence of 10 million from his dead aunt.
Daniel: He's such a Facebook Douche
UD: Stands for Unintentionally Dumb.
Adjective: A nicer way of calling someone stupid. Can be used when talking about someone that's right next to you, or telling it straight to their face.
Jack: Is he really that stupid?
Jill: Nah, he's just UD
Pam: Isn't Ray William Johnson a senator or something?
Mike: ....you're so UD