I have *terrible* luck with Canon L's....
Some examples with brand new lenses (some issues over multiple copies)...
70-200 II - decentering, broken IS, build quality issues, scratched front element, excessive CA.
35L - USM squealing.
24-70 II - decentered, scratched front element.
16-35 II - USM high pitch squealing.
17-40 - decentering.
I am sure there are more I am forgetting... I almost expect to go through a few to get good a good copy. The 16-35 issue is from yesterday! Waiting for my replacement copy now.
Are you just a lens schlimazel or does it affect your whole life?
5D IV, 5DS R, 7D II, EOS-M, Powershot G3 X, 400mm DO II, 300/2.8 II, 1.4xTC III, 2xTC III, EF 1.8 STM, EF 70-200/4 IS, EF 24-105, 15-85, 100-400 II, Sigma 10-20, Sigma 150-600mm C, EOS-M5 15-45, f/2 22, 11-22, Samyang 8mm f/2.8 fisheye