"Fun At the Drive-Thru Window!" joke
Attempt to take the order-takers order.
("Hi, may I take your order?") before they get a chance to take yours.
Order confusing items, i.e.,
"Hi, I'll have a large orange Coke and asmall medium fries, please".
When you arrive at the window to pick up your food, hand them several bags of garbage & ask if they'll dispose of it for you. Make sure it smells.
Speak in such a garbled fashion that the order-taker will think there is a problem with the speaker and ask you to order at the window. When you arrive at the window, speak in the same garbled, incomprehensible fashion.
Drive through with someone on the hood to accept the food.
Bring along a Mr. Microphone. When the order-taker speaks, aim the mic at their speaker but do so while aiming the Mr. Microphone speaker at the mic to produce excruciating feedback of their own voice.
Have a friend hide in the trunk. When you approach the window to pickup your order, have him start yelling and banging his fists on the trunk.
If you are a male, have a female friend place the order by speaking VERY seductively and suggestively into the speaker. When she finishes, have her hide and pull up to accept your order. See how many of the order-takers fellow employees have been called over to the window to "check out the babe".
Not enough votes...