I'm a huge fan of Asim but even I was disappointed with Asim's aggression.
Basically, he's really sensitive about the chela and chamcha taunts and he's been hearing these from the start from bahu gang and especially Paras.
He has clarified multiple times that he's not a chela but sid is his best friend so he'll have his back no matter what (I want him to stay away from Sid for his own betterment).But everyone still taunts him about this topic.
Plus he and Arhan have an issue from outside.Arhan himself said a lot of bad things about Asim in the news before entering the house.
Also if you had noticed in the ep that Arhan was interfing with Asim's discussions many times (like when they were working out) so Asim had built up anger that he released.
Though I agree he really over reacted and I really wish that he controls his aggression otherwise he's a good guy.