I don't get mad, but I get annoyed when i leave the store, open my bag and realize they're missing a burger.
I was in a hurry one time so I walked in since I saw like 6-7 cars in the drive-thru and only like 1 person in line. I went in there, told this under 18 looking white chick named Tiffany that I had a coupon for a buy one burger combo get one free. So it was about $10. For some reason the total came up to only around $7. Got my order in like 2 minutes after waiting and quickly left to go to my friends house. I got there, opened the bag and realized they only gave me 1 burger
I got mad for like a minute but i quickly brushed it off. There are other things to be worrying about in this world, not "oh my god i didn't get my 2nd burger", fukk this place"