Quote: "I'm not doing this for my health." O.J. Simpson, appearing at a horror comic book convention.
Figure of Speech: litotes (lie TOE tees), the negative understatement
The litotes makes a point by denying its opposite. The result is an ironic understatement, and an appropriate answer to a stupid question. "I'm not doing this out of good taste" would have made a better litotes. Still, showing up at a horror convention after being acquitted of a double murder certainly isn't healthy.
Snappy Answer: "Instead of signing my comic book, can you stab it?"