Green’s Dictionary of Slang

1. (orig. US black) to toady to, to ingratiate oneself with.

1970

in DARE.

2. (US) to inform on, to betray; thus cheese-eating n [i.e. one is a rat n.¹ (1c)].

1951		J. Blake letter 15 April in Joint (1972) 19: To report these unsavory and totally lost creatures [...] is called ‘ratting’ or ‘cheese-eating’.
1955		B. Schulberg On the Waterfront (1964) 115: People I may know . . . you mean eat cheese for ya?
1965		H. Rhodes Chosen Few (1966) 125: It’s only a matter of time ’til somebody gits hip and eats cheese, baby.
1990		R.D. McFadden et al. Outrage 278: ‘Todd is afraid to talk. Everyone will think he’s eating cheese.’ Wolff smiled at the quaint Runyonesque expression.

3. (US black) to be in love.

1970

Current Sl. V:2.