The unknown residue, usually but not always, food goo or particles on the front of someone’s shirt. Egg yolk, spaghetti sauce, gravy, ice cream, bbq sauce- something that didn’t quite make it into the mouth. May also describe similar glop left on door handles and refrigerators. It is the substance itself, not just the stain from previous incidents.
First used circa 1953 by my father noting the common occurrence of such substances on his 5 children, who still use the term with their children and grandchildren.
“You have some hustapulsit on your shirt there, Sonny boy, go put on a clean one!