Bakugou lost his hearing during the fight with villain but thankfully he survived during the fight. Everyone in Class 1-A really worry his condition and thinking he probably upset losing his hearing but when he came back to dorm, he with his usual attitude yell at everyone through sign language which make everyone relieve since there's some of them already learn the sign language. You on the other hand know that despite his usual behavior, deep down he really upset losing his hearing.