Science!

So you bought five-dollar merlot and six-dollar pinot grigio for your wine-and-cheese party, you cheap, elitist, very clever bastard. Cheese makes cheap wines taste the same. (I'd wager there's a similar effect with chocolate and coffee.)

So you doped up on haloperidol to keep your mousy, schizophrenic self from hanging out in wood chips laced with feline urine. Toxoplasma infects 1 in 2 Brits. Never would have guessed.

So you get a special thrill when watching cheaters get their comeuppance. Even better if the comeuppance is an electric shock, and you're male. Is it hard-wired or learned? Who cares? It's sweet revenge!