Jimmy's a real SOB
What, pray tell, has Howard ever done to him to warrant this treatment?
First he smashes up his car with bowling balls. Not content with that, he now sends two prostitutes to humiliate him in public, in a fancy restaurant, next to his friends, colleagues, peers - people who are (literally) judgmental and protective of their reputations. It doesn't matter if we like their rich-lawyer world. What matters is that it is THEIR world and Howard's reputation and dignity matters to him in HIS world, just as our names and our pride matter to us in our own.
So what is Howard's great crime? What has he done to deserve this?
It wasn't what Jimmy thought (and we thought) in S1 - that Howard was blocking him from working as a lawyer in HHM. That was Chuck's doing. Howard had no problems with Jimmy.
It's probably not that Howard is a handsome, rich, tailored, seemingly centered and charismatic individual. I don't see Jimmy being too upset over that. If anything, he would try to con such a person out of money, not ruin the person's public (or self) image.
This high-level trolling was triggered when Howard had the gall to offer Jimmy a job. A job that would require Jimmy to continue being Jimmy McGill, in practice if not in name.
Broadly, it seems like it is the fact that both he and Howard were hit hard by Chuck's death. Both had a sense of guilt over it. For both it was losing an older brother (literal for Jimmy, symbolic for Howard). Yet, while Jimmy can only cope by burying the past, crafting a phony persona for himself and practicing deception and self-deception; Howard seems to have gone through a tough grieving process, hit bottom, and healthily picked up the pieces. Howard is now back to being Howard; AND not only that, but he has also grown as a person. This probably irks Jimmy who just wants to destroy Howard's serenity, bring him down and join Jimmy in keeping misery company.
Whatever the rationalization, Jimmy is being a true jerk here. All he is doing is harming someone else's life for his own personal kicks.
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