Well, perhaps since I'm not gay this is far from obvious to me. And in any case there are plenty of non-sexual naked people situations where sucking a guy is definitely off-limits!
But to try to answer this, I certainly do love to suck (and suckle) women's breasts, so that would be the closest equivalent I think. I wouldn't do it unless she wanted it though, and the way you phrased the question makes it sound too coerced for my taste.