What is the X in X-mas?
c.1400, robous, from Anglo-French rubouses (late 14c.), of unknown origin. No apparent cognates in Old French; apparently somehow related to rubble (see OED). Spelling with -ish is from late 15c. The verb sense of "disparage, criticize harshly" is first attested 1953 in Australian and New Zealand slang. Related: Rubbished; rubbishing.
Something of inferior quality; nonsense (1600+)