sweeney, n. — Green’s Dictionary of Slang

sweeney n.

[the fictional Sweeney Todd, the ‘demon barber’ of Fleet Street, who sold ‘golopshious’ pies made from the flesh of those he had murdered]

a barber.

1922		Joyce Ulysses 308: Pictures of him on the wall with his smashall sweeney’s moustaches.
1995		M. Simpson ‘Prufrock Scoused’ Catching Up with Hist. 24: Do I go to the Sweeneys fer a short back-n-sides?

In phrases

go for Sweeney (v.) (also run for Sweeney)

(US) to be valueless, nonsensical.

1913		H.G. Van Campen ‘Life on Broadway’ in McClure’s Mag. Mar. 38/2: I think rich simplicity’s only proper, but if that’s her idear of a colorful night in a great city, it runs for Sweeney.
1914		‘Hugh McHugh’ You Should Worry cap. 4: Of late, however, Hep's course of true love has been running for Sweeney, and my old pal has been [...] conversing with himself a great deal.
1920		A. Baer Two & Three 27 Jan. [synd. col.] Don’t get faint-hearted if your first seven years’ efforts go for Sweeney.

that’ll do for Sweeney [var. on tell it to Sweeney! ]

(US) a phr. used in response to a piece of information that is considered unreliable, nonsensical.

1917

Van Loan ‘By a Hair’ in Old Man Curry 80: ‘Elisha has gone dead lame [...]’ ‘That’ll do for Sweeney!’ said the Sharpshooter. ‘Elisha worked fine this morning. I clocked him myself.’.

In exclamations

tell it to Sweeney! (also save it for Sweeney!) [? anecdotal or Sweeney as generic]

(US) a dismissive excl. of disbelief in a previous far-fetched statement.

1907		T.A. Dorgan in Zwilling TAD Lex. (1993) 80: (Bunk Gives The Jay Cops A Wrong Steer) Tell it to Sweeney.
1910		Wodehouse Gentleman of Leisure Ch. xxii: He says dat dat’s de woist tale dat’s ever bin handed to him. ‘Tell it to Sweeney!’ he says.
1913		T.A. Dorgan Daffydils 28 Jan. [synd. cartoon strip] Aw, tell it to Sweeney.
1919		Van Loan ‘Excess Baggage’ in Score by Innings (2004) 405: Never mind the alibi! [...] Save it for Sweeney – he’s collecting ’em.
1927		(con. 1918) J. Stevens Mattock 291: ‘He was lyin’—’ ‘Yeah, tell it to Sweeney.’.
1936		J.T. Farrell World I Never Made 477: ‘Ah, tell it to Sweeney,’ Bull Young jeered at Bill.
1947		S.J. Perelman ‘Hit Him Again, He’s Sober’ in Keep It Crisp 49: My wife’s lip curled superciliously. ‘Tell it to Sweeney,’ she said.