Green’s Dictionary of Slang

an unpleasant person; also as adj.

1970		E. Thompson Garden of Sand (1981) 457: It’s an honest livin, creep-o!
1977		C. McFadden Serial 19: He was just the kind of hypocritcal creepo Ingmar Bergman was trying to stamp out.
1988		T. Harris Silence of the Lambs (1991) 28: You old creep. Creepo son of a bitch.
1999		Indep. Rev. 24 July 10: ‘You mean Oval, Creep-o’ she said.