Green’s Dictionary of Slang

a boaster, a braggart.

1913		T.P.‘s Weekly 21 56/1: What is the difference between a genius and a swank-pot? Can’t a man be happy unless he is a genius— or a swank-pot?
1917		P.C. Wren Young Stagers 114: Goliath was a rooter, a swank-pot, a Bad Man.
1929		J.B. Priestley Good Companions 10: ’E looks a bit of a swankpot.
1932		P. Hamilton Siege of pleasure (1987) 270: He was, though not without delicacy, hsowing off. He had the makings of a ‘swank-pot‘.
1959		I. & P. Opie Lore and Lang. of Schoolchildren (1977) 202: Swankpots come in for stern disapproval [...] a swankpot is known as Swanky Liz, Swanky Lanky Liz, or Swanky Pants.
1962		K. Waterhouse There is a Happy Land (1964) 29: He was such a blinking swankpot.