Green’s Dictionary of Slang

outrageous, disgraceful, disgracefully bad; esp. in phr. diabolical liberty.

1958		(con. 1940s) B. Behan Borstal Boy 231: Why ain’t I given a chance to follow my trade in ’ere, eh? ... It’s a diabolical liberty.
1959		F. Norman Fings I i: Three days bread and water. Wot a diabolical liberty!
1961		(con. 1920s) J. Sparks Burglar to the Nobility 72: I didn’t feel anything could ever mark my card. But it did. Diabolical bad luck.
1965		(con. 1950s) B. Behan Confessions 235: A more diabolical shower of bastards it would hard to find.
1970		T. Parker Frying-Pan 46: You’re still looked upon as a human being, however diabolic what you’ve done outside is in the eyes of society.
1984		‘Derek Raymond’ He Died with His Eyes Open 53: Nothing diabolical intended, sarge.
1998		P. McCabe Breakfast on Pluto 86: It’s a diabolical liberty, that is! Frowing bombs into restaurants!
2001		G. Coughlan Everyday Eng. and Sl. 🌐 Diabolical (a): really terrible.