My friend's last name is Duffie.

The Duffies are coming over for dinner tonight.

My friend's last name is Duffer.

The Duffers went to the park.

My friend's last name is Dufaux.

The dufadars are responsible for maintaining law and order in the city.

The dufadar was responsible for maintaining order in the village.

The duffadar was responsible for maintaining order in the village.

The duffadars were responsible for maintaining law and order in the city.

He made a dufferish attempt at playing the piano.