Rex Ryan -- I'm Throwing Myself Out of a Plane!

Rex Ryan is about to jump out of a plane ... and shockingly it has nothing to do with his 4-12 record last season.

The Buffalo Bills coach hooked up with the U.S Army Parachute Team -- aka The Golden Knights -- to do a little thrill-seeking up near Niagara Falls.

Before the jump, Rex told the media ... "This is no big deal to me. I just like doing stuff like this ... thrill-seeking and things like that."

Ryan said the soldiers had given him 3 important pieces of advice when jumping -- but forgot the last two.

So, we'll see how this goes.