33, Kinda tricky but ALWAYS works. when you're out with your friends at a fast food place, when you notice their drink getting low (best if you sit away from the drink station) offer to fill it up. Take your drink and your friends to the drinks tation which is usually next to the condiments station. Open up a hotsauce (or ketchup/mustard etc etc) only the corner. Try to make the cut very small, only big enough to fit a straw into (catching on??) fill their drink up, p;ace the straw so it fits snuggly inside the sauce packet and put them both in the drink. They will never know and when they go to take a drink they will drink nothing but pure sauce!!
EASY TO DO AND FUNNY AS ****.