Green’s Dictionary of Slang

1. to convict or accuse falsely.

1947		W. Motley Knock on Any Door 207: That bastard is going to bum-rap the hell out of me. He’s going to frame me.
1959		Mad mag. Mar. 44: Us kids been gettin bum-rapped all over da lot.
1968		in B. Jackson In the Life (1972) 169: I can’t ever scream about being bum-rapped.
1972		D. Pendleton Boston Blitz (1974) 38: I don’t like the idea of bum-rapping a snatch.
1994		Rebennack & Rummel Under A Hoodoo Moon 121: You know I was bum-rap’d just t’other day [...] The kangaroo court—hah!—the kangaroo court that’s where the free man sends you to.

2. to slander, to attack verbally, to catcall.

1951		N. Algren Chicago: City On the Make 48: Can I keep my job if I bum-rap some people for you?
1967		L. Bruce Essential Lenny Bruce 109: They really bum-rapped ya, the I.R.A.
1976		E. Thompson Caldo Largo (1980) 120: You could bum-rap his wife before you could knock that goofy car.