My Step-Father, Mr. Knowitallneverwrong, used to be my greatest nemesis when I would use my family as guinea pigs. First of all, he's blind in one eye so he can only see half the illusion anyway.
During a "trial" performance of a card routine, (the last I ever showed with him around), He got his "I'm so cool" look on his face, crossed his arms, stuck his chest out so it was almost as far out as his belly and said, "That was easy, I know how you done it."
I simply replied, "OK i guess you don't need me then". I handed him the deck and went to my room to work on something else...Ah the good ole days of livin at home
About 2 years later, I was at a public performance, and who do I se sitting right in front? My Mother who is impressed by everything I do, My little brother (then age 7) who is unimpressed with anything magical since he learned his first trick, and My step-father, Mr. Knowitallneverwrong.
However, instead of trying to make himself look cool, I heard him a few times say, "Now how'd he do that?" He's never tried to tell me how i did it since.
I don't suggest this being the way to deal with an average heckler, but this was a family oriented case. And family is supposed to be supportive. From what I've been told, he actually tried to reconstruct the card trick that he "knew how i done it" and failed. Thanks Mom