when an old man hikes his pants up to his wrinkly man boobs, grabs hold of the waistband and moves it back and forth..(after telling some great achievement story that makes him proud)
Every time Grandpa tells another WWII story, he stands up and does the ole Achievement Pants move
by Granny Moses July 23, 2003
A pair of imaginary pants used as a symbol to award someone when they've done something good, but hardly worth noting. Same as in giving someone a "cookie."
"Oh, you took out the trash? I'll go get the achievement pants for you to wear."
by SM Jordan October 13, 2004