I cannot float

I sink like a brick.

That's not uncommon, especially among men. I have big bones in my legs and relatively little fat. I go down feet first, like the bow of the Titanic!

All my fat is in my head, it has it's own gravitational field.

I can swim, but I have to keep moving, like a shark.

I've known guys who could not swim under water because they were so buoyant, no matter how hard I tried to hold them under.