Green’s Dictionary of Slang

1. (US) of a man, fashionably dressed, smart; cite 1886 suggests effeminacy.

1886		Nat. Police Gaz. (NY) 30 Oct. 2/3: The little chap Hamilton [...] is said to be an even funnier specimen of an English dude [...] He wears a bang and bracelets, and is accused by those who know him to be really much too sweet to live.
1953		Kramer & Karr Teen-Age Gangs 119: His dress was in the ‘sweet’ fashion – dark, well-pressed trousers, white shirt, knit black tie with narrow clasp, blue-black corduroy jacket. Flashy clothes were regarded with contempt.
1979		‘Iceberg Slim’ Airtight Willie and Me 51: He’s sweet and loaded.

2. (W.I.) tipsy, slightly drunk.

1956

cited in Cassidy & LePage Dict. Jam. Eng. (1980).