Green’s Dictionary of Slang

chuffed adj.

also chuft
[16C SE chuff, swollen out or puffed with fat, or the muzzle of an animal]

1. annoyed, disgruntled.

2. [1950s+] (orig. milit.) very pleased, delighted, happy; often dead chuffed or ext. to chuffed to fuck, chuffed to arseholes, chuffed to buggery etc.