Green’s Dictionary of Slang

1. (US prison) to eat prison food.

1992

Bentley & Corbett Prison Sl. 67: Jug Up To eat a prison meal.

2. (UK prison, also jug) to attack a fellow inmate with a jug of scalding water.

2000		Guardian Rev. 31 Mar. 9: ‘Jug him!’ said one man (meaning to scald him with a jug or two of boiling water from the urn, mixed with sugar so it would stick).
2000		Sun. Times News Rev. 12 Mar. 3: The ‘nonces’ (sex offenders) who were regularly ‘jugged up’, meaning attacked with jugs of scalding water and sugar, which sticks to the skin.
2004		(con. 1990s) N. ‘Razor’ Smith A Few Kind Words and a Loaded Gun 352: The bloke he had jugged was a big-time drug-dealer.