We had fun at YAPC::Eurpoe (merci, Paris perl mongueurs). One particular event I remember was on the way back from the restaurant on (IIRC) Saturday evening. There were about 8 of us needing tickets, and we figured it would be better to buy a carnet of 10 than lots of individual tickets. Dan commented that his Euro coins were worthless after he left, as he couldn't change them back to dollars, so he decided to get rid of as many as possible into the ticket machine. Richard and I joined in the mad coin stuffing excersise.
Picture 3 perl mongers inserting coins full throttle into a single slot, only to suddenly find that the ticket machine as turned into a fruit machine in payout mode. Kerching, kerching, kerching, kerching! Only we've not hit the jackpot, as a helpful message on screen (in French) tells us that there's a maximum of 20 coins per transaction. Bastard machine, foiled our plans!
So we scrape out our 21+ coins from the output hopper, regroup and try again, being careful to stick to 0.50 EUR (or greater). This time we beat the machine, and were rewarded with the dulcet tones of tickets being printed.