Well.... Bossman DID confess to his audience about using hard drugs daily and needing to be held accountable because he wanted to quit. To me it sounds like his wish was granted, monkey-paw style.
Regardless who the crackhead actually threw hands with, it's pretty clear that the element which set this in motion was RatBro. Less than 72 hours after he moves in, the equilibrium in the house is disturbed. If I were to throw in my guess of what set it off, it was probably Andrew confronting Austin on the noise. "Unlike some people around here.... SOME of us actually have to get up in the morning to GO TO WORK!" And, of course that would make Austin feel some sort of way. He either could have been offended that Andrew's trying to 'take over' the house, or how DARE he suggest that Austin's online gambling (with sponsorships!) isn't a real job. Eh, it could have gone a hundred different ways. Still, it all starts with Andrew.
I bet BossMom has already received half a dozen collect calls from Austin telling her about how hard this is for him, how this time he wants to get clean, accusing her of choosing her other son over him, not loving him, etc. Anything to get bailed out. For her sake, I hope BossMom leaves the phone of the hook for the next several days.