The guy I work with. He's a maladjusted sociopath who cannot sense the moods of other people or doesn't care. He's a conversational minefield: every time you talk to him the first thing out of his mouth is "Oh for fuck's sake!" He hates his job, he hates his customers. He finally got himself a girlfriend but that didn't seem to make him any happier.
We just now nearly came to blows because he was adamant that a debit/eftpos transaction was completely different from a credit card transaction from the retailer's perspective. I maintain that both card types result in a payment into the retailer's account, so they're basically the same - for the purposes of grouping the totals on a report, at least.
He eventually won the argument by saying, and I quote, "Look, just fuck off man, it's obvious you don't know what you're talking about."
Well, one of us doesn't, that's for sure.