crack on a stick

something that is very popular and/or sells very well.

Can also be used as an exclamation similar to "oh shit"

Guy 1: How's business?
Guy 2: Great! Our new stuff sells like crack on a stick!

fall-back attack

when someone suddenly backs off after realising they are in a situation they can't handle.

Joe had a fall-back attack and ran from the fight after he realised how big the other guy was.

Skydiver1: I didn't think we'd be up this high.

Skydiver2: I can't jump. I think I'm having a fall-back attack.