Slap-Happy Sly appears in the Sesame Street song "The Ballad of Slippery Slim". Sly and his best friend, Slippery Slim, go camping on a slippery slope when his sleeping bag slips and he rips his slacks.
Slim offers to slide down the slope on his sled to Slappy's Slack Shed and get Sly a new pair of slacks. However, on his way back up the slope, the sleet and snow make it difficult for Slim to move forward. Thinking quickly, he ties a slip-knot to his sleigh, slings it up to Sly, and the day is saved!
Impressed with Slim's daring, Sly comments, "Slim's no slouch. No one's slicker than him!"