Video: The world of Counter-Strike is a dangerous place. Lethality lurks around every corner. Think that birthday balloon won't knock you dead? Think again.
They skip into a party so chill that everyone died (or left because, you know, terrorists), stand on the picnic table to get a better vantage point, and... suddenly eat it.
So, what happened? A fairly notorious (at least, among the handful of people who've experienced it) physics glitch. There are multiple possible explanations: some speculate that you get "stuck" between the balloon and the picnic table, and a slight balloon shift produced enough force to, er, kill. The most prominent (though also disputed) explanation is that you get "stuck" on the balloon, and the game engine treats it like you're airborne. When you touch the ground again, it's counted as fall damage -- sometimes a small amount, sometimes enough to kill you instantly.
The lesson? Probably just stay away from the balloons on Overpass. Bright and shiny though they might be, balloons are not your friend.