Even if you didn't know the Strong Bad Email that this spoofs, the Team Fortress children's book: "Every Class is Different," would still be a howler.
It's only a couple minutes long, and yes, the tone is a bit pedantic. But Spy reminds us of a very important truth at the end, so pay attention.
I won't spoil the best line in this video, which went up June 1; but for my money it's the one about Sniper. You can get a look at the source art over here, too.