Probably on another night, while not in the time loop, a brawl would definitely be possible. But due to all the stress and the drinks, Johnny's not in his usual head space. Jack happened to catch him at a vulnerable moment.

Johnny's face has turned bright right in the meanwhile. There's not even a chance of hiding it, but he tries. It also dawns on him that the entire bar saw that - not that they'll remember later anyway. He laughs quietly at the remark about cheering up.

"Been a rough, uh, while. Lost track of how long it's been. You... know what's going on. It's been happening to you, too."

Obviously, since this hasn't happened before. Johnny had been too wrapped up in his own worries, that he feels guilty for not trying to catch up with more people. Especially if they were aware of the effect.