I've often wondered about that myself...in USA porn. I remember about 15yrs ago, most porn stars would say things like "disgusting" or "gross" or "hell no I don't wanna taste my shit" and things of that sort if you ever asked whether they would suck the dick or toy out of their ass.
The automatic names that pop into my head instantly are ofcourse...more extreme girls at the time, who always looked to push limits. Stars like Jewel Denyle, Nikita Denise, Monica Sweetheart (who was really glamorous but always did filthy stuff and a ton of atms), or Belladonna...but I think she came a couple of years after them, She I think was part of the generation after, of extreme girls like Taylor Rain, Kacey, Ariana Jollee etc.
So I am sure some of you would know the answer...I am talking about the girls who did ass to mouth in MAINSTREAM porn...not niche stuff like FORCED early Max Hardcore stuff. The girl who did it totally willingly, and often...like it was normal (which it wasn't in porn, at the time) .