How Do I Tell People To Back Off?

[Stewy]

Sir (or name). It has been good talking to you, and I don't want to be rude, but I'm not feeling very social this evening and just want to relax with the game and my meal. Again i apologize, but I don't feel like talking to people tonight. Have a good evening.

and ignore him.

if he persists, then either remind him you don't wish to talk or move tables.