Green’s Dictionary of Slang

1. (also muffincap) a fool [? play on flat n.² (1), i.e. the muffin is a small flat cake or link to muff n.² /muff v.¹ (1)].

1818		J.B. Hart [title] The Amours of Geoffrey Muffincap & Molly Popps.
1830		W.T. Moncrieff Heart of London II i: A visitor? hurrah! some muffin, I daresay.
1842		T. Hood ‘University Feud’ in Works (1862) V 419: The members meet for that and other tuneful frolics – / And not to say, like Muffincaps, their Catichiz and Collec’s.

2. (also muffin-cap) a ‘pill-box’ hat or cap, as worn by charity-school boys; also attrib. [resemblance].

1838		Dickens Oliver Twist (1966) 86: His jealousy was roused by seeing the new boy promoted to the black stick and hat-band, while he [...] remained stationary in the muffin-cap and leathers.
1842		T. Hood ‘Tale of a Trumpet’ Poetical Works (1906) 608/2: The charity chap, / With his muffin-cap.
1844		Essex Standard 8 Nov. 2/4: Another young gentleman, an éleve of the muffin-cap school.
1856		Bucks Herald 9 Aug. 6/5: Their hats would have dwindled down to the size of a charity boy’s muffin-cap .
1869		Bucks Herald 13 Nov. 3/1: The dress of a Northampton charity boy is[...] Blue swallow-tail [...] and muffin-cap and stockings of the same hue.
1873		Sl. Dict.
1878		Derby Mercury 31 Mar. 3/7: A head-dress [...] surmounted with an embroidered muffin-cap and tassel.
1903		Portsmouth Eve. News 24 Aug. 3/1: [The] muffin-cap [...] makes an excellent quoit.
1914		Dundee Courier 3 Mar. 8/1: The Hat in Slang [...] A by no means exhaustive list would include ‘tile,’ ‘golgotha,’ ‘canister,’ ‘castor,’ ‘chimney,’ ‘colleger,’ ‘cock and pinch,’ ‘cowshooters,’ ‘david,’ ‘digger’s delight,’ ‘fantail,’ ‘gomer,’ ‘goss,’ ‘moab,’ ‘molocher,’ ‘muffin cap,’ ‘mushroom,’ ‘pill box,’ ‘stove pipe,’ ‘thatch,’ ‘truck,’ and ‘wee jee’.

3. (Can./US) a female companion who accompanies a bachelor on his round of social amusements.

1870

J. White Sketches from America in Farmer & Henley IV 378/1: When a man [...] has secured a young lady for the season, to share with him sleigh-driving and other of the national amusements, in Canadian phrase she is called his muffin., Her status is a sort of temporary wifehood [...] though [...] it has nothing in it which shocks.

4. (US) a male chaperone.

1865

G.A. Sala My Diary in America II 159: Throughout the voyage that male person is the lady’s ‘muffin’ [...] and generally fetches and carries after the manner of a Newfoundland dog.

5. an incompetent, one who is awkward.

1867		Ball Players’ Chronicle 11 July 6/3: The muffins (poorest players) of the Trimountain Club played a match game of base ball on Friday afternoon on the South boston common [DA].
1871		L.H. Bagg Four Years at Yale 45: Muffin, an unskilfull player at base-ball.
1925		S. Lewis Arrowsmith 361: Joust [...] was straightaway discharged and replaced by a muffin.
1939		R. Chandler Big Sleep 145: You’re no English muffin yourself.
1973		C. Gaines Stay Hungry 184: Crayag, you were such a muffin.

6. (US gay) in pl., the buttocks.

1972

B. Rodgers Queens’ Vernacular.

7. in pl., small female breasts.

1972

R.A. Wilson Playboy’s Book of Forbidden Words.

8. (US campus) an admirable person; usu. in combs, such as stud-muffin under stud n.

1976

P. Conroy Great Santini (1977) 30: Gee, thanks a lot, muffin.