Princeton rub, n. — Green’s Dictionary of Slang

Princeton rub n.

also college fuck, Princeton first-year

[a practice attributed to freshmen at Princeton University; note Rodgers, The Queen’s Vernacular (1972), ‘It was alleged that college men, wanting to explore homosexuality, would refuse to actually penetrate one another for fear of turning queer; so, they turned to a position which most resembled heterosexual coitus’]

(US gay) body-to-body rubbing; intercrural intercourse; thus Princeton style adv.

1972		(ref. to late 1950s) B. Rodgers Queens’ Vernacular 30: college fuck [style] (late ’50s) the act of rubbing the penis against the flat stomach muscles of a partner until orgasm. [Ibid.] 154: Princeton style (fr a ‘popular’ recreation pursued in British boarding schools and American ivy league dorms) fucking the thighs.
1988		H. Max Gay (S)language 33: Princeton style—to ejaculate by friction between another man’s thighs.
1999		Gaymart.com Queer Sl. in the Gay 90s 🌐 Princeton Rub – Intercourse between two men in which one’s penis rubs between the other’s thigh, or between the two men’s abdomens.