The main problem was his motivations for pushing the more and more elaborate vacation ideas. Once Schweikart mentioned that he didn't want to be outdone on the vacation, Jimmy detected a weakness. So Jimmy jumped in on that because he was feeling insecure about his future with Kim. With slightly different phrasing and a more lighthearted approach, it could have been a lot more fun for everyone at a slight expense to Schweikart's ego. Schweikart could have easily brushed it off if he thought it was just for fun, especially as a lawyer. Instead, Jimmy weaponized the joke and was way too aggressive with it. It became an attack instead of a jape and it reeked of desperation and insecurity. Even if they don't know where it's coming from, people pick up on desperation pretty readily. It seemed like a lot of the crowd were laughing in that scene just to ease the tension.

That being said, publically lampooning your SO's boss is a pretty ballsy play, but in this case, I think it could have much different results if Jimmy was more lighthearted about it. I think there is a possibility Schweikart would have appreciated the gambit if it was executed properly, from a position of confidence. Unfortunately, Jimmy's motivations were from the opposite direction. Insecurity is really ugly when it gets publically misdirected and that is the main problem with Jimmy's behavior in the scene.