The guy who enters the room while you're watching a movie and then ruins the ending.
Based off of the Greek dues ex machina meaning the "God of the machine" that would enter the play near the end and solve all of the problems the characters would have.
Guy 1: Hey you watching a movie?
Guy 2: Yeah, it's The Sixth sense.
Guy 1: Oh, I love how Bruce Willis is dead at the end of this movie!
Guy 2: Thanks douche ex machina
A geeky person who's become overly confident with the opposite sex. These people tend to treat their significant other with less respect than when they were not so confident.
This usually happens because geekiness has become more socially acceptable than in the past, and more people are attracted to geeks then ever before.
Boyfriend: Wow, there are so many hott chicks on my facebooknow!
Girlfriend: Your such a douche nerd lately.