You get all kinds in a library. Someone (I have no idea who, but I have my suspicions) peed on the floor of the mystery section about once a week. That was fun to clean.
Then there were the parents that would complain about the quality of the food at programs, or that the craft was "cheap". Um...this is the FREE public library. You get what you pay for. I would like to point out here that the library was located in an affluent, country club community. We got a mixed bag, about half the patrons were wealthy and half were the people that were employed by the wealthy people. It was only the wealthy people that complained about the "value" of things at the library though.
There was an older man who came in nearly every day and he loved to argue. He was a crotchety get-off-my-lawn type and could complain endlessly about everything and anything and would monopolize my time for hours if I let him. I kinda loved him, but on the really busy days i wished I could make myself invisible.
Public libraries seem to attract a large proportion of mentally ill people. It's a low stress environment so mostly we got along great, but there was one man who was a regular, he had schizophrenia. He went on and off his meds, but he really only spent time in the library when he was off his meds and homeless. He had incidents with a couple of us; he once went off on me, lunging at me, yelling and swearing in my face because I had no idea that there was a baseball game that evening--the smallest things would set him off. That incident ended when he pushed me and (bless his heart!) another male patron grabbed him and hauled him away from me. We had to ban him not long after that because he went off on a patron and threatened to shoot them.
I left the worst for last, and this goes beyond "annoying". I had one patron who couldn't keep his hands to himself. He started out making lewd comments, then he got brave and groped me in the stacks a few times. It was particularly scary because it was a small library and I was often closing up with only one of the part-time teenage library pages, and we didn't have security. He had an infatuation with me and would lurk in the parking lot at closing time, or sometimes he would be waiting at the door for me when I opened the library, which I did alone. It escalated quickly and my boss had to get the police involved. The whole thing was shameful and embarrassing and scary and even as I'm typing this I'm shrinking into my seat. I quit not long after. The official story was that i quit because I was pregnant and wanted to stay home while the kids were young, and that is true, but my encounters with this man factored into my decision too. I loved my job but I didn't feel safe at work, and there wasn't any feasible way for me to feel safe again. We couldn't afford to hire security or more staff.