Green’s Dictionary of Slang

a swaggering braggart, also adj.

1590		Three Lords and Three Ladies of London C: What a brag boy is this to comparison with a man, but boy [...] I will lay six Ballades to six ierkes at your buttocks, that you shall not sing so well as I.
1635		J. Gower Pyromachia n.p.: Thou Braggadocio; thou (quoth hee) / Dar’st thou doe any thing with mee? / Th’art nothing but tongue-courage, now I see.
1640		Wits Recreations n.p.: On a braggadocio. Don Lollus brags, he comes of noble blood, / Drawn down from Brutus line; 'tis very good!
1654		W. Day Exposition of [...] Prophet Isaiah 126: [C]onsider what Rabshakeh was, an Infidel, a Vaunter, a Braggadocio; and then it is no wonder to see him so inconstant in his words.
c.1698		B.E. Dict. Canting Crew n.p.: Brag, braggadoeio [sic] A vapouring, Swaggering, Bullying Fellow.
1725		New Canting Dict.
1741		Braggadochio, or, His Worship, the Cully [play title].
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue n.p.: braggadacio a vain glorious fellow, a boaster.
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.