What would it entail to program a mod that...
 

...would make a pop-up with check box when a poster hits submit reply or submit thread that makes them click the check mark saying they got their girlfriends permission to post?

I was thinking of doing something like this for a friend of mine who is extremely whipped. Im new to anything programming, so how difficult do you think this would be?

:D

Pretty simple, you can use if conditionals to match your friends userid or username, then when he is on that page, it will pop up.

You'll just need some popup code.