rude, rude, rude

Why am I always the one thanking people that are ringing me up at stores? Often,I also tell them to "have a nice night!" It's not my job to be the nice one when I am shopping at Food Lion. Sometimes I try and be rude just to see if it has more impact than when I am nice, but the cashiers don't seem to notice whether I say one word to them or not. I know what it's like being a cashier at total crap jobs, and I always loved it when people decided to be nice to me. Maybe I should just start pretending to talk on my cell phone the whole time anyone rings me up.