I've been known to do this from time to time with D&D. Someone once invited me to join a random game just to screw around, so I made a commoner who was specced and geared to have something like a +40 bonus to Use Magic Device checks involving scrolls. (I don't remember exactly what level he was, but he certainly shouldn't have been casting 9th-level spells)
I hope to use him again in another not-so-serious game, as I rather enjoyed playing a fake wizard.