What bothers me the most are people who repeatedly insist that Canon's L series zooms provide IQ that is every bit as good as Canon's L series primes - even when confronted with test evidence to the contrary. Specifically, people who say the 100-400 is just as clear as Canon's big supertelephotos such as the 500 f4, the 600 f4, the 800 f5.6, and the 400 f2.8.
I also hate those.
Along those lines. I slightly get miffed when people compare zooms to expensive primes (expecting a zoom to be as good or forgetting that zooms are sometimes more handy/cheaper than primes). Zooms and primes are different animals.
Like saying someone should get a 200 f/2 IS instead of a 70-200 2.8L IS because it's better.