The service was fine. In fact the cashier was actually pretty friendly. But, if there is one thing that will cause me to never go back is...
When you order something specific and you get all the way home to find out it's wrong. So it goes into the trash... 8 bucks down the drain... And you make yourself a bowl of cereal.
Now, with all the talk about folks working at fast food that think they should be making $15/hr: this is exactly why you don't. You had one instruction to hold the mayo and you failed.