In general I love all my bikes as I only ride for leisure so each ride is usually very enjoyable - I avoid bad weather.
However, when I had a brake issue with my new CrossTrail, I actually hated the bike for a while. I spent weeks trying to resolve the brake issue by myself and then managed to strip the threads in the rear brake calliper. I had no option but to hand it in to my Specialized shop who sorted out the brake issue for me. Now all is well. I'm a bit of a perfectionist so any imperfections on my bikes tend to play on my mind.