There's not much of a meaning is joke. The joke explains itself:

in yo mouf

The action of completely submerging ones testicles in peanut butter(creamy or crunchy) then someone gobbles gurgles and wipes clean the nutsack to the point of shine.

An engulfing ejaculation so powerful that it will not only blow your dickhead off, but it will stretch your dickhole so far that everything dribbles out and you can make hand signs with the excess skin.

having the best possible high and low hands in any split poker game, i.e. Stud 8 or Omaha 8.

v. The act of ejaculation.

n. Semen.

For a man to Come, semen coming out of dick.