Green’s Dictionary of Slang

duck’s arse n.

also duckass, duck bum, duck-fanny, duck’s ass, …butt
[SE duck + arse n. (1)/ass n. (2)/bum n.1 (1)/fanny n.1 (3)/butt n.1 (1a)]

1. [1950s+] (orig. US) a type of hairstyle, esp. as adopted by teddyboys and rockers, in which the back of the hair is turned upwards in a manner similar to a duck’s tail.

2. attrib. use of sense 1.

3. [1990s+] (Irish) a soggy cigarette butt.