People knitpicking your car.
63 Dartman got it right: "I've had such a great time building my car and learning that it just doesn't matter."
I have been playing with this stuff for darned near 40 years. Trust me, the people who nitpick wouldn't know a lug nut from a sloane valve.
My personal favorites are the ones who look your car over from fender extension to quarter panel extension, and then proceed to go on for hours about their wife's uncle's brother's neighbor's cousin's Chevy Monza that came with vinyl seats that looked JUST LIKE imitation leather! Arrrgh!