Pithy on a rock bun

Can anyone tell me who Pithy on a rock bun is and the meaning?

I don't know what a pithy is but to feel like a piffy on a rock bun is to feel left out or deliberately ignored.

"I simply can't believe that I'm being made to stand here like piffy on a rock bun until some barmaid notices I'm gasping for a pint"

Thanks for the link, Carmen!