Green’s Dictionary of Slang

fraggle n.

[the 1980s TV series Fraggle Rock]

1. (UK prison) a homosexual man, esp. when forced into the 'passive’ role.

[UK]R. Black Hard Time 115: ‘I’m not going to kill you Travis… I’m going to make you into my own personal fraggle. My bitch’ [Simes:DLSS].

2. (UK prison) someone who is mentally disturbed.

[UK]Sun. Times News Rev. 12 Mar. 3: His roomies were the ‘cluckers’, ‘toppers’ [...] and ‘fraggles’ (mentally disturbed).

In compounds

fraggle flops (n.)

(UK prison) prison-issue trainers.

[UK]G. Krauze What They Was 261: Don’t wear prison-issue trainers, mandem call them fraggle flops and don’t rate you if you rock them.