the best one is to walk in and order something thats clearly not on the menu

dude walks in to McDonalds
dude: ya, id like the lobster rolls
cashier: sir, we dont have lobster rolls here
dude: what are you talking about, there right there
dude points to a random place on the menu on the wall
dude: RIGHT THERE, number four, the lobster rolls!
cashier: sir, number four is not lobster rolls
dude: what, are you calling me stupid now?
and so on...

i do it all the time, but its soooo hard to keep a straight face