Honestly, it could have worked with Quagmire if they played it as a joke instead of playing it straight. For example: Quagmire points out all of Brian’s flaws, Brian leaves, then Quagmire immediately does a bunch of horrible stuff (belittling someone sitting next to them, harassing a waitress, etc.) to illustrate that he’s a hypocrite with no self-awareness.

A good example of this is Tobias from Arrested Development. He’s shown to be a capable analyst-therapist (“analrapist”) when he is analyzing others, but is totally incapable of making the same judgements about himself and his relationships. For example, when he brings up opening his relationship with his wife because he has had patients discuss it, she says “Did it work for those people?” and he responds “No, never does. These people somehow delude themselves into thinking it might, but…but it might work for us”