What does Boxing Day have to do with boxing?
expression of contempt, 1929, from Yiddish, from German pfui (attested in English from 1866); popularized by Walter Winchell. Phoo "vocalic gesture expressing contemptuous rejection" is recorded from 1640s.
(also phoo or pfui or fooey or fooy or fuie) An exclamation of disbelief, rejection, contempt, etc
[1929+; fr Yiddish fr German; popularized by the newspaper columnist Walter Winchell]