I’ve heard some doozies but here are some of my favorites:

1. Show up drunk.

2. Show up very sweaty in your gym clothes (unless you are trying to be a personal trainer or something where this would be remotely acceptable).

3. Guys, if you notice your interviewer has a picture of a young girl, ask if she is ready to start dating. Ladies, do the same for pictures of young boys.

4. Ask if two and three hour lunches are acceptable.

5. Ask when they allow you to start working three day work weeks (this works best for full time positions).

6. Chew gum loudly and with your mouth open. Finish it off by taking it out of your mouth and putting underneath the table/desk you are sitting at. Make sure the person interviewing you sees this.

7. Sit back, prop your feet up, and ask when the massage is coming.
CNN offers a more serious take here as does this source here.

Seriously though, relax and be yourself without looking like a nervous wreck. An interview is a two-way street – they need to make it look like a desirable job to have also! Ask plenty of questions of them as well!

Good luck!