The mayonnaise did it for me.
Years ago we had a small fridge at work which was meant to be used for milk only. You know what those Brits are like with their tea.
We had a Belgian colleague who received a special dispensation from the boss (in the spirit of multicultural tolerance, because he had to have it for his chips) to keep mayonnaise in the milk fridge. He stuck a label on it with 'I can't believe it's not milk'.
I'm much more likely to put mayonnaise on my chips than milk in my tea, that is if I ever drink tea.