Selfishness
This has driven me nuts when people abuse the overhead space by squeezing their jackets, bass, and their mini backpacks/LV bags. It's no doubt carry-on limit has to be enforced, but what frustrated me the most are the following:
1. I saw a bass in FC overhead bin. That took up the entire row of overhead bin. I had to call the FA up to get a rid of the bass.
2. I always saw people (Even in FC or elites) who boarded early put all their stuff on the overhead bin above row 1/2. In AA, it's 3/4. I am getting sick of having to move my carry-on at the back of FC or even in Y cabin.