Help me decide what to put on a mug for my friend! I have until midnight PST.

So there's this particular custom T-shirt/etc website that I love, which I won't name here in case people think that I'm spamming. I've been mulling over what to get a close friend of mine for Christmas, and I decided that since he loves coffee, I would get him a mug from this website and fill it with some candy canes and goodies from Starbucks. You can never have too many mugs, right?

Well, today, this website is having a 50% off sale on mugs and T-shirts. And since the other presents I'm getting for people from this site are T-shirts, THIS MAY JUST BE MY LUCKY DAY! However, now I have until midnight PST to decide the perfect slogan or graphic to put on this mug to make it perfect for my friend. Can Reddit help?

My friend is geeky, and something of a gamer. He smokes a lot of pot. He's a big libertarian (one of the things I'm considering is "There Ain't No Such Thing as a Free Lunch"). He loves sci-fi/fantasy novels like Discworld and Iain Banks, but I don't know anything about these so I would have no idea what reference would go over well -- perhaps someone into these novels could assist? He loves webcomics like Penny Arcade and Achewood (I was also considering putting the Stoned Lightning logo on a mug, since this would combine our mutual love of pot and Achewood, but I would rather shy away from copyright infringement if possible). I will try to add anything else I can think of about him.

Suggest away!