If a woman feels extremely uncomfortable with it, those are her feelings. Many women are former rape or molestation victims. I don't like the idea that any sex act should always be OK with everybody.
Whether it's criminal is a different story, but it being a problem and not 'OK' for every woman is understandable, I think. I can see why it feels like too much lack of consent to some women.
It's the sort of thing that should be discussed at some point beforehand, I think. In a playful way, sure, but to check out the waters before going there some morning (with penetration or oral, anyway)!