I ask a variation on this: "tell me about the program you're proudest of." And also: "What's your favorite algorithm or data structure? It doesn't have to be

I ask a variation on this: "tell me about the program you're proudest of." And also: "What's your favorite algorithm or data structure? It doesn't have to be the fastest or best, just your favorite? Why?" (This does have one right answer: shellsort.) "Tell me about a time you made a mistake — not a time where one of your weaknesses turned out to be a strength and you saved the day. No. Tell me about a time you really screwed up."