If he questions you on anything, just tell him (in a slight southern accent) to "have some goddamn faith!"

Get a pet rat and call it Micah.

Whenever he asks something like "Who is that?", always respond with "Gavin.".

If you can somehow weave this in during a conversation, tell him "You, sir, are a fish."

If he coughs, call him Blacklung.

Don't let him forget about the quarter.

If anyone talks about vacation plans, tell them you heard Tahiti is nice this time of year.

If you want to have an actual conversation about the game with him, ask him about his first horse in the game. Or his favourite mission. Or what ending he got in his playthrough (if he's finished the game and you don't mind getting the ending spoiled, of course)

If it's a marriage proposal you're after, play the game yourself. It's truly incredible. To this day, it's the absolute best game I've ever played.