Ive had some costs in my time but this should make you laugh

[flammableBen]

My old uni housemate who's name was Kirk was always trying to think up ways of generating cash (my favourite was drunkenly stolen things on ebay). Someone told him that if you don't take your money quick enough then the cash point sucks it back in. Fair enough. For some reason Kirk presumed that it would automatically add the amount back onto your balance, and had an imspirational idea of a way to fool the bank into giving him free money.

His plan consisted of withdrawing £40, carefully taking one of the £20's and then letting the cash machine take back the other one, and in Kirk's head fooling it into cancelling the withdrawal and leaving the entire £40 in his bank.

Pretty enterprising, although of course it didn't work. Kirk was left having to explain to  the bank how he only managed to take one £20. I'm not sure if ever got it back. I'll ask him next time I see him.

[lebowski]

that's very close to something called reversal fraud, which does work.

you would have to be incredibly stupid to do it on your own bank account though.