I'm a waitor at a restaraunt and to be quite honest with you, if you come in looking like trash, you get bad service, BUT I have my certain characteristics that I look for to determine if I'm going to give them bad service:
1) if you come in and I've served you before and I know you don't tip, then they'll just get the worst service in the world (and NO I wouldn't ever spit in the food or shit like that, just no refills and really really slow and rude service)
2) if the person is wearing ANYTHING with the confederate flag on it
3) if the person is wearing ANYTHING with Nascar on it
4) if the person has a mullet
5) if they are rude to me regardless of what you look like
6) if they are missing teeth (unless they are really polite)
7) if they look like they are in high school
8) if they are wearing dirty t-shirts
9) if they are wearing John Deer hats
10) if I just get the "I'm not getting a tip from this table vibe"
People really PISS me off when I give them good service and they leave crappy tips, I'd rather have fun with them and give them horrible service and not get a tip so they will be reluctant to come back.