Green’s Dictionary of Slang

scarlet n.

[a synon. for blood n.1 (1)]

an upper-class ruffian.

[UK]J. Shebbeare Lydia (1769) II. 437: I expected to have seen her [...] encouraging the young bloods, bucks and scarlets at a riot in Drury-lane, the most distinguishing and newest Mark of a Lady ' of Quality.