Green’s Dictionary of Slang

1. the seated rump, usu. as symbolic of laziness.

1953		L. Uris Battle Cry (1964) 127: Off your dead asses and on your dying feet.
1960		(con. 1950) R. Leckie March to Glory (1962) 24: It’s about time we got off our dead asses and earned our pay.
1971		J. Contini Beast Within 126: He’d better get off his dead ass.

2. an idler, a lazy person.

1960

(con. 1940s) G. Morrill Dark Sea Running 149: Look lively, you dead-asses.

3. one who is effectively dead; cit. 1967 implies a state of impotence.

1959		B. Hecht Sensualists (1961) 126: I was always a dead ass [...] Built for men. Every inch of me. They go crazy when they hold me, naked or dressed. And me! A lot of foam rubber without a nerve ending. Dead.
1967		N. Mailer Why Are We in Vietnam? (1970) 14: Usa women know which man has got the spring and who and which is the unfortunate dead ass.
1975		E. Torres Carlito’s Way 88: Lllod, he is a dead-ass, don’t let’s get weighted down with him.

4. a listless, de-energized person.

1968

T. Wolfe Electric Kool-Aid Acid Test (1969) 50: Trying to get some action going among these deadasses in the loony bin.

5. an utterly boring, useless person.

1960, 1975		Wentworth & Flexner DAS.
1989		(con. 1960) P. Theroux My Secret Hist. (1990) 177: So long. Dead Ass.