ok here is one
Customer: I want a nemo fish
Me: clownfish are marine fish do you have a marine tank?
Customer: Its an all glass tank.
Me: I mean the type of water it lives in is marine, do you have a saltwater tank?
Customer: I'm not adding salt for a fish. it'll be fine.
Me: It wont survive in fresh water.
Customer: dont talk to me like I am an idiot. I have kept fish since I was ten.
Me: I'm sorry maam, I'm just trying to make sure you have the right stuff to keep the fish healthy.
Customer: Its my money, If it dies, whats it to you? Your job is to sell me the damn fish! Now bag it!
Me: sorry maam, but I cannot sell you the fish knowing it is going into fresh water that would be against the law. have a nice day.