1st 叫主 used offensive language such as “烏合之眾” to describe other people and then people started to attack 叫主 by making bad jokes. ("Subject :一幫人胡說八道"- Very offensive)
2nd They used coarse language because 叫主's offensive language made them want to "attack" him.
3rd 叫主 should say sorry first and then it's their turn to say sorry.