So wouldn't you be acting like the "know it all"? Just saying. If you "hate people that think they know everything." then you are probably on the wrong forum to begin with. lol. Most people here think they know everything when in fact all they know is what they've been told or taught. That's all any of us know. So why would you waste your time arguing with someone that you KNOW doesn't have a clue what they are talking about? Who cares if the dude thinks his heating rock is the best? Honestly? Is it your business? If you don't wanna hear it, then say your goodbyes and walk away. It pays to be the bigger person.
As goes for this entire post, I was taught if you don't have anything nice to say, don't say anything at all. Instead of telling everyone your story, maybe you should have educated the person at the pet store. If he persisted to think he was right, then just leave it at that. Call him a moron on the ride home. Personally I think it's pretty shallow to post up on the forums about how stupid/ignorant/moronic, etc you think someone is. Instead kill them with kindness, make him know he's a moron. Prove to him he's wrong. Then, walk away.
My 2 cents.