The Jerome stuff was all well and good, but what was the deal with the Quagmire parts? He hates Brian and goes on a huge rant to explain why, but it doesn't make any sense. He accuses Brian of lusting after Lois but Quagmire does the same thing (remember when he was making a sex-doll version of Lois from stuff in her garbage?). He then lords his own volunteer activities over Brian and insults his dating habits with women. All of it can be summed up by saying that Quagmire is a judgmental jerk who should keep his mouth shut.
Prior to the rant, he shoots down all of Brian's attempts at humor or small just mean, not even funny.
The worst sin though is that the Quagmire stuff just isn't funny. It's watered-down "reality TV" style interactions that have no place in this kind of show. I get that it's fake, that this is all just a cartoon, but if you're going to do this kind of "real situation" where Quagmire straight up doesn't like Brian, it has to be SOMEWHAT funny. They're trying to take a flat character - Quagmire - and turn him into something more, but it makes no sense.
This is the second worst episode of the show, right behind the one where Stewie and Brian are trapped in the bank vault. They're trying to add in "serious" stuff, and it just doesn't work.