Yes, COXCOMB is a Scrabble word!

Letter values in Scrabble US: C 3, O 1, X 8, C 3, O 1, M 3, B 3.

Is it a valid word?

COXCOMB is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

a conceited dandy who is overly impressed by his own accomplishments
a cap worn by court jesters; adorned with a strip of red
the fleshy red crest on the head of the domestic fowl and other gallinaceous birds