Floyd Mayweather Jr. -- The Royal Penis is Clean

Everyone knows Floyd "Money" Mayweather Jr. leads a lavish lifestyle, but this is INSANE -- video of his assistant giving him a bath ... and it's no big deal to Floyd.

The clip is straight out of "Coming to America" -- Money has a female assistant sponging down his back as he sits fully nude in a bubble bath ... brushing his teeth!

Floyd posted the vid on Instagram Thursday morning ... which, unfortunately, means it's limited to 15 seconds. He added the caption, "This is how I get my day started, everyday. - MR. MY LIFE IS THE SH*T."

We can't argue ... and neither would Prince Akeem.