We had an older gentleman come in to shoot on our range. We have a printed copy of our range rules that shooters have to read and initial, so they know what they can, and can't do. For some reason, so many people read the questions out loud while they're answering them. One of the questions asks how much firearms experience you have. He read it and answered aloud "I qualified Expert in the Army, so I must be an expert" (he was Nam-era). He then asked for some 20ga slugs for his slug gun. Five minutes later, he was back at the counter b*tching. "These shells won't shoot in my gun. It's probably because they're 2 3/4 and my barrel says 3 inch". I went out on the range to see what was wrong. He had an 870 slug gun and the barrel looked kinda big. I looked, and sure enough, it was a 12ga. The bad part of retail is you can't embarrass a dumbasz customer too much, but it was good for a laugh.
I was in a Gander Mtn one time looking at ammo. This guy walks up and is having a LOUD phone conversation with another guy. All I klow is I heard .308 Norma Mag on the other end of the phone. Guy grabs a box of .308 Wins and says Don't worry i got you some ammo. He started to walk away and I said those wont work in a .308 Norma Mag. He turns around and tells me they say.308 right on them. I told him for .308 Norma mag ammo hes going to need a reloading press or a time machine but those .308 Wins wont work. He walked away with the shells.
That's awesome!