Sounds like you have great managers. I've worked in food before and I have to say they are correct. Lots of people are assholes in restaurants. It helps to decompress with your coworkers and sometimes customers next in line will go "what was her problem?!" Which always made me feel better.
I was working retail at a CD/DVD store in college on a particularly busy Saturday with a coworker and two managers when an older man asked me for help finding Bette Midler stuff for his wife. I looked up what he was looking for in the computer and went to show him where her CDs were, when he told me he had been looking for her movies. I didn't (still don't) know any of her movie titles off the top of my head, and our indexing system has no way to search by actor, so I looked her up on IMDb on my phone and started searching individual titles, clearly going above and beyond for this guy.
We had a couple of the movies, but before I could go find the guy my manager needed me to hop on the register for what turned into a five minute long line of customers. I was just about to have sometime else go help the guy when he's the next person in my line! So I say "oh, did you find what you were looking for?" About to explain that I had been about to send someone over to him when he says "yes, no thanks to you!" and unleashes a tirade of curses upon me. I stood there stunned, totally not expecting this from a previously very pleasant man, but it was just "fuck you, fuck this, this is shit, etc."
One of the managers (second in command, relatively new to management) was at the register next to me just as floored as I was. My store manager came running over from the other side of the site, told me to move, and took over. He told the man that he would not be purchasing the CDs (I guess he had settled for the stuff I had shown him earlier) and that he was not welcome to come back to the store ever. This was a big deal because a five CD transaction would be great for our numbers. Well the man did not take kindly to that, and he fought back. It was his right to buy the CDs, other such things. My boss told him to leave numerous times, but he was firmly planted in front of the register. Eventually my boss did the transaction and told the man that if he ever came back the police would be called.
Once the man left, my boss apologized to me for what had happened and for letting him by the CDs, but he figured by the end that it was the easiest way to get him to leave. I told him not to worry about it and explained what had happened. He then politely lit into the second manager for not taking action himself. My second manager apologized later in my shift for not stepping up, saying that he was shocked but that it wouldn't happen again. I told him not to worry about it too much as I was just as floored, but thanks. That was by far the worst customer I've ever had.