He didn't fly home with the team, which apparently is a huge no no in the NFL and has never happened in 35+ years by any coach (I personally don't see the big deal here, but it is).  He cancelled team meetings which pissed people off.  He "apologized" then another video came out showing his apology was not geniune.  And probably the biggest thing...he is 0-4.  I bet if he was 4-0 the uproar wouldn't be so big.