Ahh, go right ahead. I expect you are correct in most instances.
Well, I only met him that once, at a reception arranged by a colleague. I was responsible for hiring him to come over and do a yearly seminar at NYU. My predecessor had set the thing up, and I didn't see that my own preferences should govern--it was an obvious coup for the department.
Anyway, I don't really know what was going on, but in my view of academia (not personal experience, however), sleeping with the professor and getting good recommendations are not necessarily irreconcilable. But what Derrida was actually up to I have no idea. All I could think to ask him was whether his apartment was comfortable and he had everything he needed.