I was traveling from Orlando to Cleveland for thr '97 NHC via commercial airline. A friend asked me to carry a corny keg of beer for him to be entered in the keg-only competition. He assured me that the pressure had been released from the keg. When I got to the check-in counter the attendant asked what the keg was. I told her it was beer, and all of the pressure was released. She proceeded to take her pen and use the point of the pen to push down the poppet valve on the outlet side of the keg.
Beer sprayed everywhere, including all over the attendant, me, the ceiling, the counter... Standing there with beer dripping off of her chin, the attendant said, "That's pretty tasty, what kind of beer is it?"
We cleaned up the mess, the counter attendant apologizing the whole time, me embarrassed and pissed off that I hadn't checked the relief valve. The keg was checked in, but as the baggage crew brought the keg out to the plane, the pilot spotted it and refused to allow it on his plane. It was carried to Cleveland later on a cargo-only plane, and my friend won third place in the competition.