A while ago I gave a gorgeous studio lady a leisurely backrub (my favorite way of starting a session) then asked to go down on her. She declined, with this explanation: "Oral is for a relationship." In my hobby career and elsewhere, I've often been reminded of the last line of an old joke: "Not in the ass, mister! I'm saving that for the man I marry!"
What's the strangest thing you've ever been refused by a provider, on the grounds that she was reserving that particular activity for her SO?