One time I had my paintball guns compressed air tank in my check in bags, which was prefectly legal at the time as long as it was empty (I havent checked the laws these days, but im guessing it is not allowed).
Well of course I got called in to have a little chat, and to my complete surprise, they were in the room trying to figure out how to get the tank back together after disassembling the valve. I expressed my extreme displeasure and pointed out that had the tank had any air pressure in it whatsoever, the valve would have shot out like a bullet towards the person who was no doubt looking right at it
. On top of that these idiots were trying to put it together upside down. I was livid, but there was really nothing I could do but move on and be glad that at least they brought me in to ask me how to fix it.