Green’s Dictionary of Slang

1. (also blow one’s own horn, toot one’s horn) to brag, to boast.

1832		Satirist (London) 17 June 197/2: Another came to blow his horn, / One famed for his disguises; / He showed the liveries he had worn / Of various hues and sizes.
1870		Essays and Reviews (Princeton U.)37: From the knowledge of Castner's character, gained by careful observation, we have always considered him perfectly capable of ‘blowing his own horn ’.
1871		Gardener’s Mthly Aug. 244/2: He is averse to ‘'blowing his own horn;’ but good skill requires as much advertising before it is known as the Quack's business does.
1880		Medical Gaz. 407/2: Dr. Swinburne [...] certainly is an adept in ‘blowing his own horn.’ If all that is stated in the report is to be belived, Dr. S. would appear to be the leading surgeon of America, if not of the world.
1885		M. Davitt Leaves from a Prison Diary I 150: Young thieves would, of course, ‘blow their own horn’ in narrating their sentences and exploits.
1900		F.P. Dunne Mr Dooley’s Philosophy 18: I think Tiddy Rosenfelt is all r-right an’ if he wants to blow his hor-rn lave him do it.
1938		W. Winchell On Broadway 15 Oct. [synd. col.] Remember when only the columnists used to toot their horns about their scoops?
1968		‘Hy Lit’ Hy Lit’s Unbelievable Dict. of Hip Words 3: When one is barking, he is bragging, blowing his horn, chest-beating about his greatness.
1979		E. Torres After Hours 181: ‘I don’t want to toot my own horn, but the appellate courts have used some of my briefs verbatim’.
1992		D. Burke Street Talk 2 187: Every time I see him, he blows his horn.

2. (US) to speak or sing out of turn.

1837		A. Greene Glance at N.Y. II ii: lize.: And if it wasn’t for bein’ in the street, I’d sing it for you. mose.: It’s too early in de mornin’ for many folks to be out – so you’re safe. Blow your horn.
1897		A.H. Lewis Wolfville 251: I reckons Billy’s merely blowin’ his horn; bein’ sick an’ cantankerous with his game knee.