Green’s Dictionary of Slang

1. (US prison) an individual who first gains parole and then returns to the same prison after breaking the terms of that parole or committing a new crime.

1983

R. Klein Jailhouse Jargon and Street Sl. [unpub. ms.].

2. mutual oral-genital stimulation.

1967		M. Braly On the Yard (1977) 278: Whatever sissy she would pick out on queen’s row to turn flipflops with.
1971		E.E. Landy Underground Dict. (1972) 80: Flip flop...Simultaneous oral copulation.

3. (also flippy) a homosexual who takes either the active or passive role in sex.

1971–2		C. Shafer ‘Catheads [...] and Cho-Cho Sticks’ in Abernethy Bounty of Texas (1990) 204: flip- flop, n. – a homosexual who plays both male and female roles.
1975		J. Carr Bad (1995) 136: Flip-flops, also called ‘knickknacks,’ are dudes that begin by making the homos but wind up playing the female roles themselves.
1996		L. Pettiway Honey, Honey, Miss Thang 27: My preference—no. I would prefer him being on top. I would be more submissive. If I had to deal with one of these flippies [...] I could put up with him for a couple of months. [...] That’s not what I want in a relationship. A flippy! [Ibid.] 197: I had a relationship with a man and he was a flip-flop. He was a man ... well, he carry himself as a man, but I got the kitty. [...] And I’m a drag queen. I’m a transvestite.

4. (US) a change in personal style.

1991

B. McCarthy Vice Cop 103: ‘People know who I am, how I operate. I haven’t exactly been quiet about it. And I doubt that they would buy a flip-flop at this point’.

5. (US campus) a bisexual.

1998

Eble Campus Sl. Nov. 3: flip-flop – indecisive person; bisexual.