John,

I went on YouTube and searched "Vance gets booed at Kennedy."
These popped up in the 1st batch of videos.
I picked AP because it leans left and NYP leans hard right.
The videos were similar.

I SUSPECT, GUESS, SPECULATE...

Most were democrat machine. Trump has upended their world and they hate it.
A few may be Old Guard, Uni-party Republicans. "The senator's club." They hate what Trump has done to their influence. They can't get into places now that they became accustoming to "owning."

All have been part of the DC club for years and Trump is tearing it down using Blitzkrieg tactics.
And the finger in their eye is that Trump has now appointed himself to oversee the presentations at the KC.

So yeah, there were some boos. But not that many.

Marty

https://soundcloud.com/sunset-poet-of-texas