Scratching your arse and smelling your fingers

British • Verb Phrase
Intentionally doing something you know will cause you pain or emotional discomfort, just in order to feel something.

Person 1: This tastes absolutely disgusting.
Person 2: Why are you still eating it?

Person 1: ... I'm not really sure.
Person 2: You're just scratching your arse and smelling your fingers then, aren't you?