Kermit the Frog, n. — Green’s Dictionary of Slang

Kermit the Frog n.

[rhy. sl.; ult. Kermit the Frog, a character in The Muppet Show (1976–81)]

1. a lavatory [bog n.¹].

1998

2. sexual caressing, stopping short of intercourse [snog n.].

1998

3. (N.Z. prison) an inmate who rarely leaves their cell [? dog n.² (1b)].

2001

D. Looser Boobslang [U. Canterbury D.Phil. thesis] 98/2: Kermit the Frog n. an antisocial inmate who spends most of his time alone in his cell.