I agree. I hate when people try and prove you wrong or embarass you when you are trying to help them.
A few years ago we were giving a demonstration when a rather large athletic guy was giving my friend a hard time when he was showing a wristlock during the hands on.
The guy basically put a death grip on his wrist with all his might so naturally the lock didn't work.For those of you who don't know they don't work that way exactly,especially if your opponent is stronger. I had him grab my wrist when he did I politely slapped him with my other hand and went into the lock from there. He was a little nicer after that.
You are right,never give them the opportunity to embarass you.