Green’s Dictionary of Slang

1. a euph. for fucking adj.

1969

L. Hadow Full Cycle 141: ‘He’s a bit rough, isn’t he?’ Frank said quietly. ‘Too muggin’ right he’s rough.’.

2. annoying.

1974

G.F. Newman You Flash Bastard 49: There was no way those felons were going to pull clear of the jewellry store and escape; that in the event would have been too mugging after the way Sneed had nursed this blag.