Green’s Dictionary of Slang

1. a lazy person.

1972

Milner & Milner Black Players 47: A poop-butt is a lazy person, a ‘drag-ass’.

2. an uninformed, unsophisticated, immature person.

1969		Cressey & Ward Delinquency, Crime, and Social Process 807: A ‘rowdy, loud mouth poop butt’ making trouble at a party will shatter the common mood of sociability.
1972		E. Folb Urban Black Argot 143: Poot-Butt a ‘square’, someone who doesn’t know ‘what’s happening’.
1976		R.H. Coombs et al. Socialization in drug abuse 164: The most severe threat to any adolescent drug user is the ‘snitch,’ or the ‘loud mouth poop butt’.
1980		E. Folb Runnin’ Down Some Lines 19: You got yo’ li’l ol’ pootbutt, yo’ square brain, he don’t know wha’s happ’nin’.
1985		T.R. Houser Central Sl. 41: poot butt [...] Not as severe as an asshole, but one who essentially can’t hang.
1993		L. Rodríguez Always Running (1996) 140: ‘I don’t speak Spanish.’ ‘It’s mostly English, poop butt,’ I responded.

3. a general term of abuse.

1985		T.R. Houser Central Sl. 41: poopbutt Nonchallenging, but demeaning expression for a person.
1990		S. Morgan Homeboy 73: Both of you pootbutts. On the floor.
1996		Eble Sl. and Sociability 51: The compound poop-butt for ‘an undesirable person’ doubly defies taboo by combining a word for ‘excrement’ with one for ‘buttocks’.