Water displacement and the male body.

Funny question. I think the water level would rise a bit, because the blood that fills the penis when it's erected is probably coming from places where it doesn't affect the volume of the body (you probably know the old joke, that this blood comes from the brain).

I believe that the answer is yes, the water level will rise. There is a constant blood stream in the penis, not only during erection. The difference is that during erection the veins in the penis a partially blocked by the artery and some of the blood "stays" instead of going back to the heart. The next logical step is to say : "Ok, so there is less blood in the rest of body", IMHO the answer for that question is No as in situations like erection the heart beat rises anyway and supplies more blood to the body, as in blood loss situation.