No never, most of my girlfriends were old fashion when it comes to sex and I never dared to try, with my last ex I had a feeling it might be allowed, since she is pretty much sexually.... errr, let's say somewhat loose and hotblooded. But with me somehow, she did want to go into certain aspects of the sex game, too bad for me. I did try once like you said, and I got a slight taste of her asscrack by making my licks slightly longer. That was nice, she was rather sweaty also since she came home from a long run, kinda spicy and salty...and god I loved her smell down there, very musky but not dirty. But the second my licks got more and more directed to that zone, she did not let me go through with it.
I tried weeks later one more time, lied on her stomach, kissed from her back down and further, but again she stopped me. Too bad, I so love her sexy ass......