Green’s Dictionary of Slang

arrogant, conceited.

1817		W. Cobbett Works XXXII 43: The upstart, big-bellied, swell-headed farmer can bluster and bully [...] about Sinecures. He can swear and rave on this score like a madman.
1875		Arizona Sentinel (Yuma, AZ) 8 May 4/1: I can knock the socks right off’n these swell-head teachers.
1878		Leeds Mercury 1 Nov. 6/2: A big swell-headed Turk.
1881		Salt Lake Herald (UT) 29 Nov. 4/1: The ex-congressional greenbacker the swell-head Rev. De La Martyr.
1884		Salt Lake Herald (UT) 26 Jan. 2/1: This swell-head Governor.
1890		‘Cad McBallastir’ Society as I Have Foundered It 46: John Smith, my Newport Swell-head chum!
1891		Princeton Union (MN) 23 July 4/1: He is a swell-headed demagogue or a senseless ass.
1907		Commoner (Lincoln, NE) 15 Feb. 9/2: A more insinuating, swell-headed class of people than the Japanese [...] would be hard to find.
1910		Sun. Times (Perth) 12 June 4s/5: He is not swell-headed, but he is impulsive.
1912		A. Berkman Prison Memoirs of an Anarchist (1926) 199: He’s the rottenest sneak in the dump, a swell-head yap.
1927		(con. 1910s) S. Lewis Elmer Gantry 347: These folks need the gospel just as much as the swell-headed plutes out on Royal Ridge.
1933		M. Marshall Tramp-Royal on the Toby 287: The author is the most conceited, boastful, swelled-headed egoist who ever wrote!
1941		K. Tennant Battlers 155: She, a member of the aristocracy, to be tipped by a swell-headed, jumped-up farm-hand.
1954		E. Hemingway letter 10 Nov. in Baker Sel. Letters (1981) 839: That’s no reason to act swelled headed.
1961		T. Ronan Only a Short Walk 137: He’s that swelled-headed [...] that he thinks he’s got more power than the Commissioner.
1979		G. Swarthout Skeletons 64: He was a swell-head son of a bitch.