I want to suggest you a funny idea how to play trick on passengers of a subway or suburban train at April Fool's Day! If your friends and you are adventurous guys, you will like this trick!
So, get to coach car with your friends, pretending that you are not together. In some time, after the train departs from the station, one of you should come to the button of communication with engineer, and pretending that pushes the button, say quite loudly that people hear you: "Hamburger and big Coca-Cola at the car number…" (the number of the car is written near the button). Having said this, wait for the next station, when your friend will come at the car and ask: "Who did order hamburger and Coca-cola?". (It would be nice if the "seller" will wear uniform with coca-cola logotype). Pay off and take your "order". In some minutes again come to the button and say: "Till terminus without stops". The reaction of passenger is indescribable!