Ah, I totally feel for you, Sporkie. >_< I've got a few not-so-otaku buddies that drive me mad with their random anime choices too.
If he can handle Naruto, I guess that at least means he can take those long running anime series. Have you tried other Shounen Jump things like One Piece? (By the way, does subbed or dubbed matter?)
Cowboy Bebop and Champloo strike me as sort of masculine animes. XD Maybe Bacanno! or Berserk?
Does he like video games? I know a lot of gamers who won't touch anime, yet will cave when they see something based on their favorite game. The Devil May Cry anime was good and there's plenty others based off of games.
Hmm, I know a lot of anime and non-anime fans love FLCL. It's a bit crazy, but it's short, so you could easily make him watch the whole thing. XD If that works out too, go for the anime Gunbuster 2. If he likes that or is entertained by mechs... make him watch something Gundam or Gurren?
I'd definitely give him Hellsing. xxxHolic is really fun too. If he doesn't want to start the whole series, maybe give him a taster with the xxxHolic movie. I've never shown that to anyone who didn't like it. Higurashi (When They Cry) is also super addicting. I love making non-anime fans watch it and then they get so hooked they have to sit there for 4 episode to finish up story arcs. XD
Comedy... most people have already said what I wanted to. I think comedy or light-hearted things are generally best for people not totally into anime. I randomly think Shin-Chan can be pretty funny and it's not hard to get non-anime fans to watch it.
^^; Anyway, good luck. >:D Hope you can better convert him to all our dark ways.