Diet?

I: "Do you want some strawberries and cream?"
Boyfriend: "Yeah I want!"
I: Spoons cream into a bowl.

Boyfriend: "Not so much cream, I'm on a diet." Gets a Tim Tam.
I: "I thought you said you were on a diet?"
Boyfriend: "I was going to have two Tim Tams, but I'm on diet so I'm only having one. I'm a swapper. Instead of two, I'm only having one tim tam."