You were a member of the League of Villains and witnessed Dabi getting mad while arguing with Shigaraki..

Dabi had been arguing with Shigaraki which is a common occurrence. They normally fight over very petty things.

Today they were fighting as usual and Dabi, being himself, opened his mouth to scream.

Just that he opened his mouth so wide some of the staples fell out of his face and started bleeding, ripping his cheeks open.

Dabi: "NOW LISTEN HERE, YOU CRUSTY BASTARD!!"

He was yelling at Shigaraki despite the fact he just ripped his face open.