Interview prep tells us that the interview is a chance to show them who you are, beyond what's on paper. If your initial response to a question is humorous (within taste), why wouldn't that be appropriate, especially if the question is an icebreaker? We're not supposed to be robots - the notion that a small amount of humor somehow indicates that you're not taking the interview seriously is ridiculous. That being said, one corny joke with a self-depreciating smile is about as far as I would go.
If it was the first thing they said as I walked in the room, my response to the chair question above would be to ask the interviewer if they were a doctor/med school student - if yes, then to ask if I could sit in their lap.
With regard to some of the other interview "transcripts" (the one that mentioned the orchestra, the one about going to yale, the one where the interviewer seemed bored), your job as an interviewee is to communicate with your interviewer. You have to actively participate in the conversation - if the conversation is drifting away from your application and why you are there, move it back. Engage your interviewers. Watch their body language - are they bored, are they tired, have they already made up their minds? Your interviewer is the one who presents your application to the full committee, so you can't afford to be shy.
If the interviewer had already made up his/her mind to reject me and was waiting for the interview to end, I would at least ask why and ask what I should do differently for next time.
Oh, some crazy questions/situations:
I got one during the winter where the interview was held in this stuffy room with the heater turned on full blast. The interviewer asked if I could open the window, but when I went to open it, the window was stuck shut. I didn't know it at the time, but the window wasn't meant to open - he just wanted to see how long I would try.
I also got one where the interviewer asked me how often I masturbate. True story. I said, deadpan, "Not as often as I deserve."
A friend told me about a panel interview where there wasn't a chair for her to sit down, just a table with three interviewers seated behind it.