Green’s Dictionary of Slang

1. a black eye.

1821

Egan Life in London (1869) 73: He was fond of a little sport, and, at times, not very nice in ‘kicking up a lark’ in order to produce it, and ‘an ugly customer’ was frequently the result.

2. an unpleasant, menacing individual.

1827		Exeter & Plymouth Gaz. 23 June 3/2: Sanders, a private in the Guards, had a turn-up with Thorn, an ugly customer.
1828		N.-Y. Enquirer 15 Apr. 2/4: The Coalman has proved himself an ugly customer [in a prize-fight], and not to be rashly encountered by Jonny Raws.
1836		N.Y. Times 9 July 2/4: He shewed fight when taken but found the Police to be a more ugly customer to him than even Vanderzee was.
1840		Salt River Jrnl (Bowling Green, MO) 12 Sept. 3/2: Baer, the bukeye blacksmith, proves and ugly customer .
1842		T. Hood ‘Turtles’ Works (1862) VI 5: And now they pass that House that is so ugly / A Customer to people looking ‘smuggley.’.
1857		H.S. Brown Manliness 17: [of a dog] If he meets a savage-looking dog he calls him an ‘ugly customer’.
1858		A. Mayhew Paved with Gold 13: He stood nearly six feet high, and was a big-boned, ‘ugly customer’ of a man.
1866		J. Greenwood Little Ragamuffin 259: Mr Bobby, findin’ the ugly customers he had to deal with, [...] was playing possum.
1873		J. O’Connor Wanderings of a Vagabond 43: Let me tell you, there’s some ugly customers among that party.
1884		Kansas Cowboy 23 Aug. in Miller & Snell Why the West was Wild 615: He was [...] about as ugly a customer as need be seen anywhere.
1891		B. Mitford Weird of Deadly Hollow – Tale of the Cape Colony 99: A leopard is an ugly customer to tackle at night.
1895		Crowe Aus. Sl. Dict. 90: Ugly, cross; obstinate, malicious, as an ugly customer.
1900		Marvel 21 Dec. 10: It might be an ugly customer who rode so late.
1910		Wodehouse Gentleman of Leisure Ch. vii: ‘A man broke in, my dear,’ he said. ‘This gentleman was passing, and saw him.’ ‘Distinctly,’ said Jimmy. ‘An ugly-looking customer!’.
1916		C.J. Dennis ‘Introduction’ in Moods of Ginger Mick xi: See ’im? A narsty chap to meet! / ’E’d be an ugly customer alone an’ after dark!
1926		‘Sapper’ Final Count 852: The bird I was talking to [...] would have been an ugly customer by himself.
1936		G. Greene Gun for Sale (1973) 16: An ugly customer all right.
1946		Mezzrow & Wolfe Really the Blues 45: He stood outside [...] keeping one eye peeled for the cops and ugly customers.

3. used in fig. sense.

1847

Northern Star 23 Oct. 1/6: Tomkins, what very ugly customers figures are !!! How they do tell tales and make the black ink blush.

that member of the garrotting team who actually does the choking.

1862		Birmingham Dly Post 26 Dec. 3/4: ‘We worked our “garotting business” [...] the man [...] who put “the hug on” was called [the] “Ugly Man”’.
1890–1904		Farmer & Henley Sl. and Its Analogues.

see separate entry.

(US) to be very unattractive.

2009

N. Flexner Disassembled Man [ebook] I’d been with my share of unsightly chicks [...] girls that had fallen off the ugly tree, hitting every branch on the way down.

(Can.) to be unpleasant, aggressive, unattractive etc.

1962		J. Quirk No Red Ribbons (1968) 133: Whiskey Jack said, ‘All Wacs take ugly pills.’.
1984		Partridge DSUE (8th edn) 536: [...] Can.: since late 1950s.

see separate entry.