Perhaps what he said after the Hamill fight. The way I see it, Hamill saying shit like "the real winner didn't win the show" is just as bad, and is what I'm sure made Bisping react that way.
Another reason, DURING season 3 of TUF, a lot of people thought Bisping was a monster, a lot of people said this. And yeah, on the show, Bisping was a monster. After he won TUF, he became the next "TUF noob" and after beating Eric Shafer decisively, people began to make up bullshit assessments like "he didn't look impressive against Shafer" BECAUSE of those words he received during TUF.
Of course being cocky has something to do with it too. But it mainly started with how people perceived him on TUF, then the Hamill incident just took it haywire.
Honestly, the guy is no better than BJ Penn or Chris Leben as far as likability. But hey, how people want to view a fighters personality is their own business.
You're just a cook...