Something is trash or really bad.
The head was so bap, I kicked her outta my car while I was still driving.
Any low-pitched buzzing sound that lets you know you've done something wrong, like the ones that:
1) let you know that you did not allow enough time for a document to download on a computer;
2) let you know that you have no money or not enough money to get on a bus or train;
3) continuously go on and off to let you know that you've dialed a wrong number on a phone;
4) make a loud sound to let you know that you've made an incorrect answer at a game show;
5) buzz to let you know that you've made an incorrect move, a disqualification, or lost a turn on an electronic game;
6) etc.
I had to ask some passengers for change on the bus because the card reader let out a bap when I put the card into it.