The Donkey of Steel
In July 1966, Lex Luthor with his newfound imp-like powers, along with Mr. Mxyzptlk take turns transforming Superboy into different things like a long-haired hippie, a monkey, and Super-Jackass. The quick thinking Super-Jackass uses his heat-vision to write "Kltpzyxm" into a nearby sidewalk, in the hopes of tricking Mr. Mxyzptlk into saying his name backwards, and therefore exiling himself back to the Fifth Dimension of Zrfff for 90 days. However, before this can happen, the mighty Super-Jackass is transformed back to Superboy (SB No. 131: "Lex Luthor... Imp!").