Green’s Dictionary of Slang

moppy adj.²

drunk.

1821		‘An Amateur’ Real Life in London I 449: Frank Harry moppy, and all of them rather muggy.
1840		T. Haliburton Letter-bag of the Great Western (1873) 203: All they are fit for now is to stick up for watch-houses along the rails, for policemen to go to sleep in when they gets moppy.
1849		Sam Sly 24 Feb. 1/2: Did you ever go to the King's Arms and call for a pint of half-and-half but what that respectable talking female behind the bar (if the least moppy) [...] always wants you to have sherry instead?
1871		F.C. Burnand More Happy Thoughts 407: Dyngwell observes, ‘That both the nautical Cockalorums have been going on the scoop, and are slightly moppy.’.
1892		Albert Chevalier ‘Yer Never Ask’d ’Im For It’ 🎵 One night we goes out on a spree, Of course ’e must git moppy.
1905		A. Binstead Mop Fair 70: He occasionally got so frightfully moppie.
1908		‘Doss Chiderdoss’ ‘A Consistent Consort’ Sporting Times 13 June 1/4: When he’s ‘moppy’ no housemaid will stop in the place, / When he’s sober they clear out also.
1915		M.G. Hayden ‘Terms Of Disparagement’ in DN IV:iii 215: moony, moppy, drunk.
1933		‘William Juniper’ True Drunkard’s Delight 226: He is [...] mopped, moppy.
1944		C.B. Davis Rebellion of Leo McGuire (1953) 161: I took a risk on a Mac who must have got moppy and given the office to a muff stool.