True. Simply not showing him tricks anymore hehehe.. Got some people who act like that around me. I just stop showing tricks to them. Not because I'm afraid that I might got busted or they will reveal/know the secrets, but because the idea of magic is entertaining and give them puzzle.

Just my 2 cents tho.

When he said you "forced" the card, you should have just agreed with him and left it at that, saying something like "No sense in me doing it again, you have it all figured out."

I would also suggest moving to a mem-deck or BCS. It would allow you to be much more transparent and eliminate the "behind the back" ploy which I find both risky as a performer and suspicious to laymen.

After performing magic for close to 40 years, I can say that eventually you learn about people. Some people cannot be entertained by magic, the view it as a puzzle that needs solving. For those folks I have some impossible puzzles.

Let me make an observation about your friend. No matter what he says, he doesn't think he has figured it out. This is why he requests you to repeat the effect. He is hoping on repetition that he will catch something he missed.

Him pointing out your flashes during your cups routine, while you may view it as rude, actually is a favor. You need to learn not to flash, even if it was only twice.

There is a psychology to performing for critical audiences, that you will need to learn before you can comfortably deal with puzzle solvers. Some magicians NEVER learn this to their constant frustration. It's not easy because your effects can become almost scientific in presentation if you don't balance the entertainment.
Someone suggested Richard Osterlind earlier, probably referring to his "cancellation technique". Read some of his writing on this. Another suggestion is to get Whit Hayden's CHICAGO SURPRISE. Not only is it a good "trick", it provides excellent insight into the psychology of effective, strong magic.

I would simply recommend not doing the same trick again and again for the same person.

Sometimes, to maintain a "Good Friendship" It pays not to
mix friendship with any form of Magic!