So the question would be something like: "What sex acts are so dirty that pornstars baulk at doing them or, if they have done them, regret having done so?"

And the answer would then be: Every porn performers has to determine his/her own limits. Some are quite restrictive in what they are willing to do; others seem to have almost no limits and to enjoy constantly challenging their own boundaries as well as challenging social conventions and taboos; yet others impose restrictions that may seem eccentric to the outsider given the other things that same person is willing to do. In every case the decision should belong to the performer. Sadly some performers have been coerced or inveigled into doing things which they have then come to regret but I don't think it is useful or helpful to dwell on such matters. When, however, the limits are those the performer imposes for him/herself, they should be respected as such - equally so whether you are unhappy that they draw the line at your particular fetish or appalled that they go beyond what you deem acceptable.

"People who like this sort of thing will find this the sort of thing they like"

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Some regretted doing cream pies.

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