Thing is, you usually don't laugh at a guy holding a six foot long pointed stick. He probably won't take kindly to it. Hell, there's a reason we know the phrase "Spearchucker", and it's not because he was character in MASH. And here's the another thing to consider. Your drunken friend clearly does not give a fuck. He is obviously one of those progressives, much like myself, who thinks the best way to deal with racism is to stop making a big deal over it. He, apparently, thinks it's funny enough to dress that way and carry around a spear. One can contribute this to the booze, but, there's only so much of that one can do. And this is ultimately where the analogy falls apart, because your friend is another person, where as Sheva is just a model with a skin slapped on her in a video game.
Ultimately, is it racist? No. In poor taste? Maybe, if you're sensitive about that sort of thing. Funny? Kinda. Blown out of proportion? Yes. In manner both depressing and funny? Hell yes.