These all really happened to me (the interviewer, in case any of you were wondering!).
1. "What is the extra chair for, my invisible friend? Ha ha."
2. (in response to teamwork question) "Nobody listened to my advice. Then half the team quit. Then I took over and got the project done just in time."
3. (Make sure your fly is zipped.)
4. I was fired from my last job because of my bad attitude. I found out I have a chemical imbalance. I'm on medication now and I no longer hear the voices.
5. I think it's only fair I tell you I'm getting married in August! I'll need that month off from the summer job if you do hire me.
More:
http://quark.physics.uwo.ca/~harwood/humor2.html