[hueving]

>"PIN number" is just a shorthand for "number that is a PIN."

No it's not. "What is your debit PIN number" is not short for "what is your debit number that is a pin".

Nearly everyone that gets called out for it isn't really thinking about what PIN stands for and they certainly don't lamely defend it with this disambiguation excuse. The context in which people ask for someone's PIN essentially never has any accidental swap with "pen" or "pan".

"Type your pan on the keypad."

"Choose a 4-digit pen."

Please, English is bad enough, don't bury it with more bullshit.