When should I not turn my rx8 off?
 

Ok so basically im aware that you should never turn your rx8 off when its still cold.

But if it was warm, and I turned it off, and then started it back up again 5 minutes later, is that bad? For example, the car is warm... i go into wal-mart, grab some milk... come back out and turn it back on again.

If it's warm it is warm, it is not going to cool off much in 5 minutes. Unless it is really cold out of course.

It's fine. Even shutting it off cold in above freezing temps should be fine if your car is healthy. Extreme cold or poor ignition or motor health is when you get problems. And I'm not that sure about extreme cold.