"favorite bug" is perfect.

I don't know how any kind of problem solver in any field does not love it when they get really baffled and then solve it.

My problem would just be remembering any particular example.

Yeah, “bugs are so painful that I suppress the memory” is not someone I want to hire. I want people who get excited when you bring them a weird bug, and who have a depth of experience to bring in when debugging gets hard.