Green’s Dictionary of Slang

(orig. US campus) a stranger; someone who does not fit in.

1967–8		Baker et al. CUSS 181: Random Boy or girl (not student) from town you go to school in.
1982		Eble Campus Sl. Fall 4: random – undesirable [...] I met up with a bunch of randoms last night.
2000		P.Howard Miseducation of Ross O’Carroll-Kelly (2004) 9: She’s a total randomer. [Ibid.] 127: [...] but basically to go on the lash [...] and score some complete randomers.
2003		McGill Reed Dict. of N.Z. Sl. 169: random Weird person or behaviour to a teenager today.
2017		L. McInerney Blood Miracles : You had to immediately go dip your dick into some randomer.
2021		P Howard Braywatch 54: A total randomer called Roderic Grainger.