touching one's genitals. can be used in various circumstances, e.g. sacktapper, sackmacker, sackslapper, et cetera. often used to insult one or to denote someone as a good friend.
"Back in my day if you couldn't fold a map right, they'd refer to you as a slackmapper"
"Those days were so oppressive they'd make fun of slackmappers in the moving pictures with "slack-face"! The hardest part is answering to your child when they ask" daddy, what's a slackmapper? "