Green’s Dictionary of Slang

(UK juv.) a fool; an unpleasant individual.

1969		Current Sl. IV:1.
2001		OnLine Dict. of Playground Sl. 🌐 dose n. 1). an exceptionally thick person or used as an insult for someone who has just done something particularly daft: e.g. ‘You dose!’.
2021		L. McInerney Rules of Revelation 271: ‘She looks like an accountant all right. Doesn’t she, Gar?’ ‘I’d say she’s a fucking dose,’ he said, loyally.