I was lucky enough that when I worked at a fairly large aquarium shop (connected to a petland but we just tried to ignore them, lol) most of the customers were really into their fish, huge discus nerds and saltwater people. I think my best stories are just my miss-pronunciations. There was the guy who kept asking me questions about our "enemas" (anemones)... thankfully another customer was nearby that I could make eye contact with to keep from busting out laughing at the guy. There was also the group of middle-school girls who were staring at the tadpoles and going "Ew wow what are those?" The one poor girl who had actually been paying attention in school told them that they were baby frogs, which the other girls of course replied with "What? No way, they're like little fish or something, they don't even have legs!"

We also had an employee who sold a giant gourami (full grown, she was a big nasty thing. I loved her) twice... and had it returned twice. He kept describing it like it had the same temperament as a regular gourami. The first time she was returned was because she killed an Oscar that was about the same size as her.

Now I work overnights at a convenience/drug store. The drunks are always interesting, for some reason they're always fascinated by our little display of pay-as-you-go phones. Had one guy hovering and asking me questions about them for almost two hours before we finally made him leave. We also had the pharmacy get robbed once, nobody was hurt and we got all the customers out before the robber had even left. The guy turned out to be my room mate's jerk-ex who lied to my mom to get her to help him get my roomie involuntarily committed to a psych ward for a couple weeks. Not really a funny story in itself, but the jerk's in jail (he already had a felony on record and he stole his dad's gun for the robbery), so now it is to me.