At the dinner scene when Robin challenges the sheriff to a duel and hit him with the iron glove, he hits him on the left side of his face. When the sheriff stands up, he holds onto the right side of his face, as if that side had been hit.
I think that the sheriff holding the wrong side of his cheek fits with his character. When he tries to talk, it comes out messed up, his character fumbles quite a bit throughout the movie - to me it makes sense that he would place his hand against the wrong cheek.
I'm going to mention something that I've noticed in a couple of other areas on the website...THIS MOVIE IS A FARCE. That means that stupid humor is expected. Iron glove + holding wrong side of face = funny. Mel Brooks is the master of the farce and I think it was written this way.