Face it, potty humor and bathroom jokes make us all laugh because they poke fun at embarrassing experiences that all can appreciate.
Everybody has glanced down with dismay into their undies at one point or another, only to be confronted with “the mark". As disgusting as it is, there's not a person on the planet who doesn't know what I'm talking about.
Case in point, all through history, the greatest literary minds have woven this concept into their works:
"God Save the Mark!" - William Shakespeare, King Henry IV
Apparently, the great Bard was such a skin-flint that he refused to throw away a tainted pair of skivvies. . . . .
"Mark where the piercing wind shoots javelin-like. . . " - George Meredith, Modern Love
Seriously, need I say more about that one? Meredith must have had some significant tushie-busting gas to have elaborated in such a way. Who hasn't been confronted with “piercing wind" that “shoots javelin-like" on one occassion or another?
"The mark of the man of the world is absence of pretension. " - Ralph Waldo Emerson
I like this one. Emerson understands that the skidmark is a common thread of the human experience, and he promotes that the man of the world doesn't carry any pretenses about it.
"Look ma. . . . I finally made my mark!" - your idiot brother-in-law
OK. That last one is my own creation.
I think that a pair of novelty undies with a fake skidmark on them would make a funny gag gift. Like for a retirement party to show the old codger what old age has in store for him. Or perhaps for a bachelorette party to show the lady-of-the-hour what the bliss of matrimony holds in store for her now that the courtship is over. . .