Green’s Dictionary of Slang

(US campus) a general term of contempt or disparagement, a weakling, an inadequate, one not attuned to the prevailing styles and priorities.

1977		NBC’s Sat. Night Live [NBC-TV] I met this pathetic lame-o [HDAS].
1993		Eble Campus Sl. Apr.
1996		Eble Sl. and Sociability 120: During 1990–92, all of the following nouns categorized someone as not attuned to the prevailing style or priorities of UNC-CH student life: [...] lamo.
1999		J. Kelman After the Fall 197: ‘That cow was a bull, lame-o,’ Molly said. ‘You’re the lame-o, bull brain,’ Max shot back.
2019		N. Walker Cherry 310: She had hooked up with some guys though and she was partying with them, but they were lame-os.