Green’s Dictionary of Slang

1. (US) first-rate, superlative.

1836		‘Ax My Eye’ in New Cockalorum Songster in Spedding & Watt (eds) Bawdy Songbooks (2011) II 25: I’ve a randy dandy, tear up, flare up, / Moke that cost me forty bob.
1840		Port Phillip Gaz. (Vic.) 10 June 3/3: The Herald [...] has appeared, to use [Mr Welsh’s] own expressive slang, with a ‘flare up’ article.
1846		D. Corcoran Pickings from N.O. Picayune 135: I drives one of those newly imported conwenient wehicles with two wheels [...] they’re reg’lar flare-up concerns.

2. (Aus.) ostentatious.

1860

Adelaide Obs. (SA) 17 Mar. 2/7: Drab [...] is the : best colour for our riflemen, inasmuch as if it be not ‘flashy’ or ‘flare up’ (I use the term which slang maketh current in our language).