i dunno if this works on the newer coke machines but in the old ones, you can make it confused
1) put 1,50$ in the coke machine
2) first press the number 1 coke then number 3 then 2 then 4 and the coke machine makes strange noises and looks wierd on the display
Dont blame me if you waste your dollar and it doesnt work! etc. steal a few from your friend to test it ^^
Happy hacking