You might not have a problem with it - but someone else might very well be uncomfortable enough that they aren't okay with doing that. In that scenario it's *okay* for them to say 'no'. It doesn't make their SO wrong for asking them to try it out...but if said SO doesn't accept that they aren't willing to do that, and keeps pressuring them for it? *That* is wrong, and that *does* cross boundaries...which, yes. I would consider hurting someone.

Think of it this way, say A didn't feel up for having sex, but their partner [B] asked if they'd want to have a round of it. When A says 'no', they aren't being selfish - just honest that they really aren't feeling up to sex. If B accepts that, then there's nothing wrong. However, if B starts pressuring A to have sex - not enough to qualify it as rape, or assult, but enough that A just breaks down and gives in because they know they'll be badgered about it otherwise? That's wrong.

In that set up, just like the one OP mentioned, it's not about 'sacrifices'...it's about being put into an uncomfortable situation that you may not be okay with. OP could be the most generous, or the most selfish, of partners...We don't know that. But either way, if the OPs not comfortable doing it, then there's nothing wrong with the OP saying 'no' to it.