Green’s Dictionary of Slang

muddy adj.

1. (Aus.) a euph. for bloody adj.

[UK]Sporting Times 4 Mar. 1/5: It’s only you poor muddy punters as can’t get proper underclothes!
[Aus]N. Keesing Lily on the Dustbin 24: Women used to let off steam domestically with a fine range of substitute expletives. ‘Holy Moses!’, ‘Holy mackerel!’, ‘great balls of fire’, ‘good gravy’, ‘jumping Jehosophat!’ and ‘muddy great bucket of pitch!’.

2. (UK Black/gang) lit. bloody.

67 ‘Beats Cypher’ 🎵 Joog em joog em for my money / Fuck a bro man get muddy.

3. see muddled adj.

Based on mud n. (4), i.e. excrement

In compounds

muddy fuck (n.) [mud n. (4) + fuck n.]

(gay) anal intercourse with a partner whose anus has not been properly cleaned.

[US]B. Rodgers Queens’ Vernacular 139: muddy fuck one who excretes during anal intercourse.
[US]Maledicta III:2 232: Other names and words [are] muddy fuck (shitty) and pack your mud.
muddy funster (n.)

1. a euph. for motherfucker n. [initial letters].

‘mark_t’ ‘Kid-o-vision’ 9 Mar. halfbakery.com 🌐 The infamous Die Hard scene where Bruce Willis is heard to shout ‘Flip you, you muddy funster’ at the bad guys (and a nation’s children turn to their parents and say ‘But his mouth didn’t say “flip”...’).

2. a homosexual [mud n. (4)].

[UK]Roger’s Profanisaurus 🌐 muddy funster n. Botter [...] anal Swampy; he who supposedly tunnels in mud.

SE in slang uses

In compounds

muddy-headed (adj.)

drunk.

[UK]W. Toldervy Hist. of the Two Orphans III 27: Tho’ we take the liberty to use harsh expressions to you, that muddy-headed fellow shan’t do it.
[UK]V. Palmer Passage 144: I can’t carry as much as the other fellows — and lately I’ve been spending most of the afternoons sleeping it off. Too muddy-headed, even, to go out in the canoe.
muddy waters (n.) [ety. unknown; ? the softness of mud]

(US black) the loss of a man’s erection before or during sex.

[US]E. Folb Runnin’ Down Some Lines 153: Terms like high waters (erection) and muddy waters (loss of erection) are graphic examples [of female evaluation].
[US]R.C. Cruz Straight Outta Compton 65: ‘Go fuck yourself!’ shouted Billy. Those words were like music to Dopehead. He reached down and grabbed his thang, standing in Muddy waters.

In phrases

get one’s feet muddy (v.)

to be in criminal trouble.

[UK]D. Powis Signs of Crime 183: Feet muddy, get your To have been in trouble, especially with the criminal law, e.g., ‘He got his feet muddy before he had straight work.’.
Old Muddy (n.) (US)

1. the Mississippi River.

Davy Crockett’s Almanack n.p.: The Great Mississippi Snag Alligator [...] I was going down old muddy one day [etc.].
[US]Omaha Dly Bee (NE) 18 Dec. 22/4: ‘Old Muddy’ is about closed tight. Vehicles crossed today on the ice.
N.O. Times-Picayune Mag. 5 June 18/2: Old Muddy undergoes a metamorphosis after she leaves the river bed [DA].

2. the Missouri River.

[US]Reader’s Digest Oct. 37/1: ‘Old Muddy,’ the Missouri River, was chiefly responsible for this flood [DA].