Best effect is if you have worked up a good sweat and your crack is real freaking greasey and if the recipient of the "shmeary" has a mustache.
Originates from an individual who frequents a lakeside "pub and grub" in South Central Wisconsin. This individual actually did this to someone who kept fucking with his father at a bar. He went to the head (bathroom) dragged 3 fingers across the crack of his sweaty and greasy ass, went out and grabbed his victim, put him in a headlock and applied the "shmeary" by using the 3 finger method. It is important to note that this dude is a pretty big guy.
According to him...
"Not everyone can just go and start handing out "Shmearys", you have to practice. You have to make sure you have a real greasy ass crack."