How to count to five.

I had to teach a customer how to count to five today. Seriously. They had two orders and the first one had 4 drinks and the second had one. I handed them one carrying tray that had five drinks on it and their food. I go on to the next order and they are still sitting at the window. They tell me I owe them another drink. I asked them how many combos they ordered. They said five. I said there are five drinks on that tray. They look at me funny like they don't comprehend what I am saying to them. I ask for the tray and count them out for them. They are STILL confused. I repeat it again.... and point at the drink and say one, two, three, four, five drinks.... you have five drinks. Again they don't get it. I repeated it again once more and still.... blank expression. They finally left and you could tell they thought I was lying to them and they DIDN'T have five drinks on the f*cking tray. This person was not f*cking with me - he genuinely looked confused.