I would say that having so many male friends around the Dude would not need to visit a doctor to get f#cked. He is postponing the visit and when he gets there, he is obviously embarassed by this change in routine. So I would be careful with the doctor theory.
Let's quote Jeff Bridges in 'How To Lose Friends And Alienate People': '[As a serious journalist] You can't ask a musical comedy star whether he's Jewish or gay. From now on, just assume they are all Jewish and all gay.'