Explaining Shoe

Shoe visits a prisoner in jail.
"It's an injustice, I tell you." says the prisoner. "I was arrested for impersonating an officer."
"What were you doing?" asks Shoe.
"Eating donuts!" says the prisoner.

Police officers stereotypically enjoy doughnuts, so the implication is that a person eating doughnuts may be attempting to give the impression that they are a police officer. The absurdity of that conclusion gives rise to the humour of the strip (if such humour could be said to exist).

Comic