Guys of all ages still just want to get toys for Christmas. So how about this Marshmellow Shooter for $16.99 at Drugstore.com? I bought my hubby two for Christmas last year and he took it to his parent's house on Christmas day to play with his brothers. His only complaint, the marshmellows get stuck in the gun after you've used them once so be sure to buy the foam pellets too.
Go big: Buy two. One for him, one for a friend. Otherwise he might spend all day shooting at you.
Other ideas for him: Sanuk sidewalk surfer shoes $55, Sony Home Theatre Soundbar $329.99 at BestBuy, Barbeque Bible by grillmaster Steve Raichlen $10.36 on Amazon, an outdoor grill, a pair of Oakley sunglasses, nice watch, iPod touch, iTunes gift card, GameStop gift card, Car and Driver or MotorTrend magazine subscription, or a bucket of car wash supplies (large sponge, squeegie, chamois, towels, hose spray nozzle, wax, carnauba wash, tire foam, wheel brush, detailing spray).