I'm getting stuck on the rude employee interrupting a conversation she wasn't involved in statement. I would hope another employee would jump in if the one I was speaking with was confused and I would be really upset if I couldn't eat ham and ended up with a ham & cheese biscuit because an employee didn't want to interrupt. I don't have an expectation of privacy when placing a fast food order and wouldn't consider the second employee to be interrupting.
She was the one in charge of getting the items from the display, she was probably waiting to see what it was that the OP wanted and hurry the transaction up with the 15 people now waiting behind her.
I had a reply typed up, and then I went to have a bath and came back and wish now I'd posted earlier...
It was a little out of my way, but I went back and grabbed a "tell us how we did" feedback card and dropped it off. It forced me to keep the details quick and simple, and let me rate individual aspects of the transaction on a scale (ie, cleanliness, speed, politeness, etc).
For those who guesses this was Tim Horton's, you;'re right. And for those who have been there, the inappropriateness of the rude employee is a little clearer to understand. I don't like calling out places by name... but I guess the fact that I've already mentioned being Canadian and needing/wanting my coffee point other Canadians to the coffee shop as much as a neon sign.

This is how most locations are set up. There is a single line for the row of cashiers (2 at this location) who take the next customer in line as they finish their previous transactions. After the cashier rings you through, your order pops up on a computer screen behind the counter and one of a few other employees put your order together. Usually (though not always, and not at this location) the cashier will make the coffee while the other employee grabs whatever other parts of your order. It's a pretty efficient setup.
Sure there were 15 people behind me when I got up to the counter, but there were 15 or so people in front of me when I got in line, too. The cashier who was serving me was putting through about 2 customers for every one that the other girl was. That's neither here nor there, but it does point to her not necessarily needing to be corrected by the employee grabbing the donuts and making the coffees. Also, since she was not limited to doing just one cashier's order (just whichever one popped up next on the screen), there was really no need for her to put her nose in - she could have just kept going with the next order on the screen while the cashier and I got sorted out.
Anyway, I left my contact info on the feedback card. I'll see what happens.