Repetitive Redundancies

Redundancy is is a good thing is certain certain situations. (<--- that sentence was not one of them) A parachute, for example, having two is redundant, yet when the first one doesn't work, no one complains about the extra. Data backup, stunt doubles, the Doublemint twins (okay, not really) are other examples where redundancy is completely acceptable and even welcomed.

Here are common examples of where it's not:

PIN number
VIN number
ATM machine
SCUBA apparatus

You're right, that last one is not so common but obnoxious none the less. And if you don't know why these are redundant or obnoxious, slap yourself.