Looks a bit mean but an amazing bit of footage…
The collective noun for a group of baboons is a congress or tribe. More recently ‘flange’ has become de rigueur among primatologists even though its first appearance was in a 1970’s television comedy.
The red swelling on a baboon’s bottom is called an ischial callosity. Despite it looking like it is in dire need of ointment it is in fact rather comfortable and allows the baboon to sleep on a branch without falling.