If you worked in the adult entertainment industry as a graphic designer would you put those pieces in your portfolio? Or would you make a "G" portfolio and include a statement that a full portfolio including nudity is available? Or do you basically treat it in your mind as 'confidential' and just would put the job on your resume but leave it out of portfolio entirely?
Common sense would indicate that:
if you are going for an "adult entertainment" related job, then do include such works in your portfolio and in your resume
if you are going for a non-adult job, then don't include such works in your portfolio or your resume.
If you regularly go for both types then by all means have two separate portfolios and resumes. And if this is the case then you're no doubt already aware by now that some clients may be uncomfortable hiring you if you are open about the "other" work you do - a job in adult entertainment can affect how people outside that industry perceive you. I probably wouldn't even indicate that your "adult" portfolio is available on request, unless you have a good reason to believe that is what they are looking for.