bomb out on (something)

1. To fail or do very poorly at something, especially an exam. I felt sure that I had bombed out on the test, so I was shocked to learn I had gotten a B+. I studied all weekend, and I still feel like I'm going to bomb out on the Chem exam. I just cannot get a handle on hybridization. Henry bombed out on the driver's test the last time around, so we've gotten him driving lessons.

2. To quit, abandon, or choose not to go through with something. I bombed out on the horseback riding after hearing about Sarah's accident. Tom keeps bombing out on our plans. Honey, your sister's annoyed with you because you totally bombed out on your promise.