This used to happen much more than it does now in "het" porn. There was a time when male performers would do both straight and queer flicks -- John Holmes and Jeff Stryker to name two off the top of my head -- and so a woman who penetrated the O-ring was not engaged in anything strange or taboo. (There is a lovely moment in "Great Sexpectations" where the wonderful Joanna Storm is reaming Eric Edwards while he is fucking another woman.) I've also found the sight of DPs (double penetrations) and twin blowjobs to be semi-queer in appearance, if not in practice. In both cases, two "straight" guys essentially have their cocks rubbed together while doing the female of the moment. Again, this happened more in the old days than now -- though DPs are still popular with certain crowds.
DP (yes, I know)