Why do people have to be so rude?

I work a few nights out of the month as a watiress. I have come across some rather rude people since I started this job. My question is why do some of the people have to be so rude? For example last night I had a table of four come in. I promptly took their order and got them their drinks and within 20 minutes they had their food. After they were done eating, I asked if I could get them anything else. The one replied, Sam needs a box. I said ok not thinking, but I knew who Sam was and clearly he did not need one. I did not take the box to them, because I was not going to be the butt of their joke. If I had taken it to them it would have made their day. But I was not going to subject myself to embarrassment just so they could have a good laugh.
Other people have been rude if they have to wait for food. But that is only because we have been busy. You can not honestly expect the waitress to drop everything she is doing and come wait on just you when there are other customers that she has.
So my thing is, do not be rude unless there is a legitimate reason to be rude.