Big Fat Meaning

(idiomatic, colloquial) Huge, colossal.

Example:   He's a big fat idiot.
  It's a big fat honor.
1918, Fannie Hurst, "A Petal on the Current" (collected in Humoresque, 1919), in Cosmopolitan, vol. 65, p. 42:
  I know a society who will pay you a big fat sum if you'll sign over them eyes for post-mortem laboratory work.
1952, Walt Kelly, Pogo, 25 August 1952 strip:
  [Porkypine:] Why, it's a big fat honor... They'll speech at you an' feed you chicken foot stew an'...
[Pogo:] But I don't like to listen to them speeches an' I don't care for chicken foots.
[Porkypine:] If yo' public is gone give you honor, son, they isn't gone let yo' personal taste stand in the way.