Scuba Diving
When I was at Uni I went on a scuba holiday to Scotland (bloomin' cold) with some mates.

We were completely reckless with our safety: Dive in the morning, spend the afternoon in the pub, dive in the evening / at night whilst HAMMERED. On one of these occasions my buddy and I spotted another pair from our group below us, so we snuck up behind them and buddy switched off one guy's air for a few seconds.

Revenge was had on him, though, as post-pub we decided to do a rapid descent dive with the intention of getting 'narked'. Dumping all bouyancy 4 of us dropped like stones to about 10m and sat on the bottom. Almost immediately my buddy goes straight back to the surface like a Polaris missile in a cloud of bubbles. The other two were laughing (not easy underwater). One of them had cracked up the emergency bottle on my buddy's jacket and inflated it!
(Dionysian Aut viam inveniam aut faciam, Thu 13 Dec 2007, 17:04, 3 replies)

Not cool!
I was laughing up until the bit about the pony bottle. But, remember from your certification class - ascending from 10m underwater to sea level, a given volume of air will double in volume if not allowed to escape. If your friend hadn't thought to exhale on the way up, he'd be dead from lung over-expansion injury.
(chase, Thu 13 Dec 2007, 17:16, closed)

I don't understand...
Sounds like a good way to get the bends. He had the pony bottle attached to his inflator? The story is a little confusing...
(Jeepgun, Thu 13 Dec 2007, 21:12, closed)

Probably feasible
Could be possible - back in the days when BCDs were called ABLJs (assisted buoyancy life jackets) they had little air cylinders to inflate them as they weren't integrated to the main tank.
Both pranks still a mind buggeringly stupid things to do, altohugh perhaps the second 'wins' by being nearer to attempted murder than a prank.
(BeatsWork, Mon 17 Dec 2007, 12:36, closed)