The Zyzaack is when you fart in another humans mouth while under water to provide them with extra air, in an effort to help them survive.
It comes from the two divers who performed this first in the pacific ocean, the divers, zyzaack and von, experienced a failure in their scubba diving equipment. and were too deep down to make it to the surface. So Zyzaack sacraficed himself and farted in Vons mouth to give him enough oxygen to make it to the surface.
(It is also known as ars-to-mouth)
"Dude, i totally pulled a Zyzaack and saved my best chum."