It's bad form to use handicap stalls if you're non-handicapped.
Bob enters a public bathroom right before a man on crutches, and notices that the only open stall is the handicapped stall.
Bob wants to go to the bathroom.
Bob waits until a stall opens up, and he uses that one.
Bob decides he can't wait, and uses the handicap stall.
The handicap person can use the stall, and Bob is able to finish his business.
The handicap person has to wait even longer, and everyone glares at Bob and calls him names.