Some of the random people who just aren't bright astound me:
A girl walked up to the counter and said, "I think your number-thing is broken" (number-thing being our system for helping customers in order). I raised an eyebrow and asked why she thought this. "Well, it's been on 5 for a long time now." I paused to take a dramatic look down the counter. "Well, I've been helping number five with these scopes and rifles for a bit. As soon as one of the two employees can help another person, we'll help number 6." "Well, will I have to wait for you to call number 16, then." *Pause* "Yeah. You'll have to wait for your number to be called."
Another one was a guy who came in and thought he'd brought his PCS orders (gotta prove Washington residency to get a handgun). He had forgotten them, but figured his authorization to drive military vehicles on post would suffice. It, of course, would not. I offered a computer to allow him to retrieve his records, which would have all the info we needed (and a helluva lot more). After repeated attempts to get it to work, he finally reset his password. Once logged in, he couldn't find the right link. Finally, he found it. He pulled up his records and was shocked to find that he was in Air Recon--he thought he was in Cav!! Turns out, as a UAV mechanic, he'd somehow missed the whole possibility he might be in an aerial reconnaissance unit (Cav was technically correct as well, but he was more specifically assigned to Air Recon).
Then, of course, are the coworkers...one of them threatened to quit because he and one other guy were closing, and that just wasn't going to be enough help. Then again, this was far more reasonable than the time he was quitting over the NICS check delaying him. Being someone who calls them in AND someone who regularly gets delayed, you'd think he'd know better than to blame the store, but he stormed out. He came back about an hour later and still had his job, so I guess he won that round.