One time I was in a 2 week training group for a remote call centre job and they set up a WhatsApp group, a few days in one of the lads lads lads decided to start a separate group chat with some of the younger guys, I pretty much left it straight away coz it very quickly turned into a group where they just bitched about the boomers in the group and I could see it going sour.
Few days later we had to pair up to do mock calls cue a couple of the people in the secondary group chat not realising they were actually in the main one when they started started ripping the pish out of the people they were with, fully slagging them off about their looks and shite like that.
It was carnage, they tried to try and play it off and say it was some big misunderstanding and I've never felt more second hand embarrassment and righteousness that I'd foresaw the danger.
They ended up being kicked off the course which was fair.