When Philadelphia received their MLS expansion team, the Union, the coach Petr Nowak asked the supporters, the Sons of Ben, to sing a song after each goal scored by the Union. The song is (Maria) I Like It Loud by Scooter with the DOOP coming in at the chorus.
Now when the Union scores a goal, the entire stadium breaks into song. DOOP is now used in every day language to express joy.
I just won the lottery! DOOP!