Turns out, playing a Spy is a piece of cake if you simply rely on what will now be known as the "puzzle gambit."
It's weirdly, uh, ingenious? I guess? In Team Fortress 2 players can apply sprays—that is, images of their choosing—to surfaces on various servers. Uncle Dane decided to become a tactical tagger, graffiti-ing walls with a basic visual puzzle that got unassuming players to halt their panicked war-charging for a couple seconds. At that point he skulked in, put a knife in one of the many parts of the human body where knives don't belong, and gallivanted off on his merry way.
The strategy was not, shall we say, unanimously successful, but it did actually work in a number of cases. If nothing else, I find that pretty hilarious, given that I don't think Valve ever planned for anybody to use sprays this way. I doubt this trick will change the face of Spy play forever (or even really have much of an impact at all), but oh to live in a world where it does.
What are the most off-beat Team Fortress 2 strategies (or gags, since this straddles the line) you've seen?