Zelo's friends are  

When Zelo introduces Yongguk, his boyfriend, to his friends they all start talking about him like he's not there 

Some call him names and some hit on him 

The worst thing is that Zelo doesn't do anything but sit there and laugh as they humiliate his boyfriend.

Yongguk tries to stand up for himself but Zelo yells at him for disrespecting his friends  

Yongguk eventually runs off crying because it is getting too much for him to deal with and Zelo's friends are going too far