A human, even a fat American, being able to effortlessly float in the Dead Sea really challenges the concept of GRAVITY...

No, it doesn't... Not at all.

So you have no fucking idea what gravity is then?

I'll give you a hint, you need GRAVITY to calculate BUOYANCY.

It's right in the fucking equation you dipshit.

Without gravity buoyancy as you know it wouldn't work and wouldn't be calculable.

P.s. fat people float better not worse you stupid fuck