Green’s Dictionary of Slang

to fellate and then spit the ejaculated semen back into one’s partner’s mouth; thus snowballing n., this practice; snowballer n., one who performs such an act.

1972		B. Rodgers Queens’ Vernacular 76: To transfer semen through passionate kissing after sixty-nining [...] snowballing.
1997		Roger’s Profanisaurus in Viz 87 Dec. n.p.: snowball v. To blow salami cigarette smoke back into the tobacconists mouth. Sort of thing.
2000		Ebonics Primer at www.dolemite.com 🌐 snowballer Definition: bitch be suckin and you bust in her mouth then she be tryin to kiss ya Example: Last night that bitch tried snowballin on me, so I slap tha bitch.