As usual, until it's not as usual

How long would you wait at a Starbucks drive-thru window before knocking on the glass?
Katy and I always stop at Starbucks for an after-dinner coffee on our way back to my house after we've had our weekly dinner. We always stop at the same Starbucks. We usually have the same cute barista, too.
Tonight, we rolled into the drive-thru, as usual. We ordered our drinks, as usual. I tripped up Katy's drink order, as usual. We got the cute barista, as usual. I used Auntie Donna's black card for the discount, as usual. The cute barista took the money, and said he'd be right back, as usual.
Moments go by. More moments go by. Moments turn into minutes. NOT ... as usual.
Minutes go by.
Finally, after we've giggled about the fact that the cute barista has totally forgotten us, and another couple minutes go by, I decide that we must take some initiative.
I unbuckle the seatbelt, bump my head on the window frame, and stand up in the driver's seat. There's no one moving around inside the store, and our drinks are sitting on the counter by the cash register. Still, no one walking around. More giggles ensue as I relay this predicament to Katy. Then, I knock on the window.
A female barista comes over to the window, and weirdly, looks down at the drinks before she glances at the window. I point to the drinks and say, through the glass, "Those are ours." Really, the look on her face was classic. Complete and utter shock. "You mean he didn't give ... ?" No.
She quickly hands us the mochas, asked to know if they were still warm enough (otherwise, she'd be happy to make fresh ones), and then told us to just sit and wait for one more minute.
Shortly thereafter, the manager (I think) popped out the window with a couple of those any-drink-for-free certificates. He gave us strict instructions to be sure to get the most expensive drink we could on the menu when we use those certificates, because they cover every drink, with no exceptions. Then, he apologized again and told us to have a good night.
How long would you wait at a Starbucks drive-thru window before knocking on the glass?
Katy and I wait 10 minutes.

But then we get free drinks out of it.