Green’s Dictionary of Slang

(Irish) a slow-witted person; usu. as no dozer.

[1741		Scots Mag. 5 June 37/2: The Dozer [...] is none of your flashy aetheistical wits].
1979		J. Morrow Confessions of Proinsias O’Toole 28: As you request, I’ll zoom to the point ... Francie O’Fallis, you are no dozer.
1995		Irish Indep. 21 Dec. n.p.: No dozer when it comes to spotting a good yarn [BS].