Ugly break-ups are so much fun.

John Thain is not taking the BofA PR campaign against him lying down. He is blazing back at Ken Lewis and crew with a level of zeal that Bank of America probably did not expect.

Where it gets interesting is that Thain’s Goldman Sachs buddies are in a position to make sure that BofA is the odd-man out when the bailout waltz stops playing. Watch and see if Citigroup’s bid to break itself up is not helped along by the feds with side-deals with still healthy players, back-stopped by the US of A, of course. Meanwhile, Lewis and BofA twist in the wind until it is too late.

Update: CNBC reported a few minutes ago that the SEC is getting involved in the question of exactly who knew what, when. At the same time, BofA is returning fire claiming that Thain was presented with the opportunity to scale back Merrill bonuses after the $15b. loss in the quarter and refused. Ah, this is gonna be fun.

Update II: Maria Bartiromo’s interview with Thain is now up at CNBC. Nutshell, what Thain knew in September about legacy positions ML held must still be hashed out, but Thain is not backing down one inch from the notion that Lewis and BofA knew — or should’ve known — exactly where Merrill stood in Q4.