Sex is a two way street and subject to an acceptable amount of compromise. So, you shouldn’t do anything you don’t want to and neither should the other participant. Having said that, you may start saying you’ll never do a particular thing, and then change your mind later for any number of reasons. Or you may enjoy doing something now which you find objectionable later. Or even just not be in the mood for a particular thing on any random day. There is no easy or permanent answer to what is or isn’t acceptable, only what how you feel at the time.
As far as porn is concerned, I’m not convinced that all men have unrealistic expectations as a result of using it. Some will, but many won’t. My wife and I watch a lot of murder mysteries, but would never think that murdering someone was acceptable behaviour., but there are a few unhinged people out there who might copy a plot they saw in Midomer Murders. We know the difference between fiction and reality.
And mentioning 50 Shades is interesting too, as most of what I’ve read about it indicates that around 70% of readers are women, and the hook is more to do with the romantic fantasy of a handsome billionaire who falls for a working girl (see also Pretty Woman).
These days, sex can be a minefield for responsible men. How can they be sure that consent has been given? How can they be sure that they won’t be accused of rape or abuse when they begin a sexual relationship with a new partner. We find it hard enough to just pick up the signals that a female may be interested in us, so we may have to tip toe carefully in the early stages until we know we’re doing the right things .. or not doing the wrong things. In this case, it might be the man’s clumsy attempt to make sure he’s not going to accidentally cross the line, but this could unfairly be misconstrued as creepy or a red flag.