It's a
sarcastic, humorous, & somewhat bitchy thing to say, when
somebody keeps complaining about an event that happened, or a situation, & they just need to get the hell
over it.
Example one -
Girl one: *crying* My boyfriend
John broke up with me yesterday!
Girl two: That's terrible, I'm so sorry!
(...7 months later...)
Girl one: *crying* I still can't believe
John broke up with me...
Girl two:
Oh for fucks sake, build a bridge and get over it.
Example two -
Boy one: UGHHHHH! I'M SO HUNGRY!!!!!!!!
Boy two: Dude, you've been complaining for 30 minutes about your hunger. Nobody cares! Build a bridge, and get over it.