A person who collects "gimcracks" is NOT a person who collects the bones of 18th century race horses. Nope, that person has an affection for "cheap" and "showy" objects of "little or no use." The word is pronounced "Jim-crack" and is similar to another great forgotten word: "gewgaw."
Apparently this has nothing to do with the creepy minstrel song "Blue Tail Fly" ("Jimmy crack corn, and I don't care!") and also has nothing to do with your friend Jim's bum.