Well, it happened again yesterday while I was playing Horse and you'll be happy to hear; I did not warn the guy. I did, however, feel bad when he typed, "I thought it was stud" (was razz instead and he was showing high cards) and yes, I took advantage of it and won.
One player typed, "go for it bunny, it's all yours". I guess the *high cards showing* player didn't realize what he was referring to, till the hand was over.