Green’s Dictionary of Slang

(orig. Aus.) a condom.

1969		A. Buzo Rooted I iii: Hammo got stuck into him, I can tell you. Laid him out like a used frog.
1978		V.G. O’Sullivan Boy, The Bridge, The River 107: A french letter, you know, a frog, stuck in her throat like a fishbone.
1990		S. Morgan Homeboy 25: What more fitting plague when frogs were scarce, Joe sniggered, than cheap rubbers.
1999		G. Seal Lingo 126: In Lingo, condoms are [...] frogs.