Steven Soderbergh
This cameo was more out of necessity than out of choice. Soderbergh wasn't too keen on playing a director in his own film (Full Frontal), but his first choices for the part all fell through. He was eventually pressed down to the wire and was forced to cast himself in the role. He goes so far as to cover his face in the final version with a black box. No credit for this director, even if it's deserved.