Years ago I was buying a Meal Deal at McDonalds in Leicester Square. For some reason I wanted a Sprite (I'd usually have a Coke), but when the girl on service asked what drink I wanted, for some inexplicable reason I relied, "Fanta" and didn't even realise by mistake until I took the first slurp when I sat down at the table
The thing is I hate Fanta, but managed to persuade my now wife that she'd like it in addition to her Diet Coke. I then went back to the counter to get a Sprite. "How may I help you?" asked the girl.
"Large Fanta, please," was my reply...
Whenever I now have a forgetful episope, my wife refers to it as me having 'Fanta moment'!