My brother and I used to take the long skinny balloons, tape them to drinking straws, run strings between two trees, and race them with the straw as the runner.
My friends and I used to take 2 liter soda bottles, fill them back up with water, and just whale on each other with them. This was back in the day when they till looked like this:
and if you pulled the black plastic part off of the bottom, it was round and the actual bottle was of even thickness. Nowadays the bottoms are thicker than the sides and would probably leave a pretty nasty bruise if you got hit with one the wrong way.
I was kind of hoping that the title implied he hacked a balloon with some Medieval weapon, but this is still cool! I'll try it next time I try to impress the ladies.
I'll imagine he discovered this at a fancy dress party some time ago and has been playing with that marballoon without sleep or changed of clothes for days.