In an interview with Mickey Rourke, Radar asked him about why he didn’t end up in Grind House. His answer doesn’t clear much of anything up:

Radar: After turning down Pulp Fiction, why did you pass up the opportunity to work with Tarantino on his latest project, Grindhouse?
Rourke: You know what? He hasn’t made any comments about it. And until he makes a comment about it, I’m not going to say anything. It just didn’t work out. And I hope that’s what he has to say. I’m just going to wait.

Seems to me that Mickey is pissed off at Quentin.