You probably won't remember doing this, but I will remember your kind service! Pulling through a drive-thru for food or coffee is one of those things that hardly ever warrants much attention on the customer's part after the fact, but I think I need to make sure other customers know that you exist. All I ordered was an iced coffee with an extra shot of espresso (I needed my coffee hit, don'tcha know).
You brought my order to the window as you finished stirring it, and you said as you handed me a straw,
"Please taste this, and make sure I got it right before you leave."
Do you know how rare you are? Do you have any idea how many times I have wanted to walk behind the counter and ring up my own order because cashiers were too busy talking to wait on the customer? Oh, not at your particular McD's-- I'm talking in general terms. Do you know how nice it is to have someone thank you for being a customer, thank you with a smile and kind service?
I hope your boss knows how nice you are :)