Our driver likes to 'surprise' his passengers with a quick snack or drink from a drive through. He will announce his intent and wheel into your driveway. In the time it takes him to rush to your speaker, we must quickly decide what we want because we know what is coming next.
If we cannot decide what we want (because we weren't given enough time), then we must sit at the speaker and try to read your menu while the driver repeatedly demands to know what we want and reject/alter/criticize/change our selections. His demands trigger the employee on the headphones to ask, "May I take your order?"
This triggers more impatience from the driver who then begins to yell at the passengers AND the person on the speaker. You should know that this driver also cannot comprehend the fact that you cannot hear him when your speaker button is engaged. So, I imagine after you ask for the order, your ears are bombarded with his loud, confused, multiple conversations which started before you finished speaking.
At this point, he begins to order before everyone has decided what they want. He waits for a confirmation of what he has said after each item is announced. He doesn't understand that you are waiting for him to complete his order. Possibly he does understand this and expects your procedures to accommodate his behavior -- we aren't sure ourselves.

When this happens, you may step away for a moment. The driver thinks you are still standing at the ready. Rather than making sure you are still at your station when he is ready to order, he starts ordering again and waiting for you to repeat each item. Of course, you may have only heard part of his order as you had stepped away to give him the minute he requested. When you repeat the part you heard, he gets even more angry if you didn't hear what he said when you weren't there.
At this point, he is shouting/screaming. I know his volume is likely causing a lot of distortion on your end. This requires you to ask him to repeat himself for clarification. He begins to scream at the speaker, sometimes with the door open for emphasis.
I try not to think about what is done to our food while we wait, what our children are learning from this experience, or what this is doing to the person on the other end of that speaker. . . .
But I do think about all of that. I just wanted you to know we admire you for putting up with it and for always greeting our embarrassed group (with the angry driver) with a smile and offering to help him in any way you can. We will continue to try to find a solution on our end, and we continue to be grateful for your patience and understanding.