"Poem: 'Manners' by Howard Nemerov from Trying Conclusions.

Manners

Prig offered Pig the first chance at dessert,
So Pig reached out and speared the bigger part.

'Now that,' cried Prig, 'is extremely rude of you!'
Pig, with his mouth full, said, 'Wha, wha' wou' 'ou do?'

'I would have taken the littler bit,' said Prig.
'Stop kvetching, then, it's what you've got,' said Pig.

So virtue is its own reward, you see.
And that is all it's ever going to be."