Butt-Scratchers are what Peter sold to help pay for Chris's education in "No Chris Left Behind". He would sell them at a baseball game in an vendor-like fashion yelling, "butt-scratchers!'.
In "Baby, You Knock Me Out", a barker can be heard yelling "Buttscratcher!" in the audience at the Deirdre Jackson/Lois Griffin fight.
In "Peter's Sister", a Butt-Scratchers vendor can be heard at the New Haven Coliseum during Peter's wrestling match with his sister, Karen Griffin.