I'm the assistant manager at a retail store so I get to deal with most of the angry/stupid customers. I honestly usually have the patience of a saint. We sell ribbon by the yard, and once when a lady asked if she could have 3/4 a yard and I told her its by the yard only she asked if that was because I "don't know how to measure 3/4 a yard". I didn't even break the veneer of politeness. I talk a lot of shit after the transaction to my coworkers, but my boss actually usually hands crazy stupid customers to me because she has a serious attitude problem.
The only time I literally had to leave the floor and have someone else help someone was this Russian lady who was using our machine to make copies of pictures. She wanted to do some complicated stuff and I was helping her and some of the pictures didn't turn out how she wanted. I told her she didn't have to pay for anything she didn't take with her and she thought she should get to not pay AND take them. And the pictures where of her granddaughter and she apparently was really supersticious because she didn't like the idea that we would destroy the copies she didn't take. After 30 minutes and explaining to her 75 times that this is the policy and that our copies are counted, so if they aren't paid for and aren't reconciled at the end of the night, we get in trouble, I had to push her on someone else because I was literally about to explode in her 70 year old face. She came back to use the machine a couple of months later and I hid in the office until she left.