Okay, I've been meaning to post this for a while, because it comes up in my job a lot. We all know many people say things like ATM machine, to which you can snidely reply "Automated Teller Machine Machine? You don't say the 'machine' after the M! Haha! Stupid you!" whatever.
I get annoyed at that. Yes, the machine is already in the acronym. But 'ATM machine' is said enough to be common usage, IMHO.
But the one that comes up at work is "VIN number"; a vehicles "serial number", or spelled out, Vehicle Identification Number. So yes, the above would be "Vehicle Identification Number Number".
So why do I say "VIN Number" when referring to it? Because not everyone knows what a VIN is. When you say "VIN Number", they can usually figure out you're asking for that real long combination of digits. Sometimes I try to avoid the issue by saying "Vehicle's serial number"; but then the car people act snarky and go, "You mean the VIN?" (with the 'haha I'm so smart and you're stupid tone in their voice).
So, here's Fazor's PSA for the day; Next time someone says a superfluous word at the end of an acronym, don't just assume they're stupid and don't realize they don't know it's unnecessary.