Green’s Dictionary of Slang

1. an act of oral sex.

1905–07		Bawdy N.Y. State MS. n.p.: ONE FEMALE SUCK-OFF, Stone all in Mouth, – $1.17.
c.1935		‘Betty Co-Ed’ [comic strip] in B. Adelman Tijuana Bibles (1997) 58: One female suck off stones in mouth ... 1.50.
1995		Letters to Penthouse V 278: A two-way suck-off is just what the doctor ordered.
2001		‘Randy Everhard’ Tattoo of a Naked Lady 123: That stupendous suck-off would’ve been enough to make any other man [...] happy.
2019		‘Enjoying Cassie’ in asstr.org 🌐 Damn! What a suck off! She left me drained and gasping for breath.

2. (US) a despicable person, esp. a toady.

2006

F.X. Toole Pound for Pound 175: In your ass, you chink suck-off!