Green’s Dictionary of Slang

(US black) an uninformed, unsophisticated person; as adj., out of date.

1972		E. Folb Urban Black Argot 144: Rootie-Poot a ‘square’, someone who doesn’t know ‘what’s happening’.
1980		E. Folb Runnin’ Down Some Lines 39: The expression pootbutt — and its synonyms rootiepoot, rumpkin, rookie, wethead, junior flip — refers to a socially inexperienced person.
1985		T.R. Houser Central Sl. 45: rooty poop A sissy [...] ‘He ain’t nothin’ but a punk ass rooty-poop.’.
1992		R.C. Cruz Straight Outta Compton 58: ‘Who you calling crazy?’ ‘You, rootiepoot!’.
1998		Eble Campus Sl. Apr. 8: rooty-poot – corny, out of style, unappealing: ‘That song is rooty-poot.’.