Pleased as Punch
Greatly delighted. Our old friend Punch is always singing with self-satisfaction in all his naughty ways, and his evident “pleasure” is contageous to the beholders.
“You could skip over to Europe whenever you liked; mamma would be pleased as Punch.”-
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
More on Pleased as Punch from Infoplease: