Green’s Dictionary of Slang

1. a clumsy, embarrassing or highly unpleasant person.

1931		J. Hanley Boy 30: You flamer, I know why you were late.
1962		H. Livings Nil Carborundum (1963) Act II: Every flamer ... except Taffy, and he’s too dense to have any malice in him.
1967–8		Baker et al. CUSS 118: Flamer A person who always fools around.
1974		Eble Campus Sl. Mar. 3: Richard Nixon is a flamer.

2. anyone who commits a major social error; thus the error itself.

1967–8

Baker et al. CUSS 118: Flamer A person who always does the wrong thing. [...] A person without much social or academic ability.