A guy who is very narrowminded when it comes to sex-positions and/or unatural sexual tendencies. Mr. Missonary will despice all positions except the missonary position, and will have a hard time dealing with people talking about other positions or talking abouth their love towards, oh lets say horses.
Dude: "Oh man I'm so gonna watch some horse-pr0n tonight!"
Guy: "I fucking hate you now - alot!"
Dude "Oh chill Mr. Missionary"
Chick: "David totally skullfucked me last night - he's so thrilled about me getting that glasseye"
Dude: "That's so fucking wrong - I fucking hate you evil bitch!"
Chick: "Whatever you say Mr. Missionary..."