Green’s Dictionary of Slang

1. self-assertive, usu. as neg. but see cite 1952; thus bumptiousness n.

1803		Mme D’Arblay Diary (1891) 4 177: No, my dearest Padre, bumptious! no, I deny the charge in toto.
1849		Dickens David Copperfield (1991) 87: I heard that Mr. Sharp’s wig didn’t fit him; and that he needn’t be so ‘bounceable’ – somebody else said ‘bumptious’ – about it.
1851		Lytton My Novel (1884–5) I Bk IV 286: ‘Bumptious is bumptious, and gumptious is gumptious,’ said the landlord, delighted to puzzle the parson.
1861		(con. 1840s–50s) H. Mayhew London Labour and London Poor I 205/1: I can tell a gentleman, too, by his way of talk, ’cause he’s never bumptious.
1865		G.A. Sala A Trip to Barbary 150: Poor Albert Smith, than whom, with all his occasional bumptiousness, an honester and more clear-sighted hater of snobbery and shams never lived.
1870		Hotten Sl. Dict.
1883		H. Smart Hard Lines II 43: It was all very well while he was fresh, and [...] bumptious enough.
1896		G.F. Northall Warwickshire Word-Book 38: Bumptious. Arrogant, conceited.
1915		M.G. Hayden ‘Terms Of Disparagement’ in DN IV:iii 213: bumptious, arrogant. ‘English people think Bernard Shaw is bumptious.’.
1938		X. Herbert Capricornia (1939) 46: He learnt that he was a [...] bumptious fool.
1940		M. Marples Public School Slang 39: Impudent [...] bumptious.
1952		J.H. Griffin the Devil rides outside 312: [A] country dance with a bumptious, buxom, giggling girl.

2. (US black) short-tempered.

1893

Shand MS Speech n.p.: Bumptious [...] The Negroes [...] use this word to mean irascible, easily angered [DARE].