incredulous (adj) - skeptical, disbelieving, or unable to believe [in-krej-uh-luhs]
BREAKDOWN: IN- (not) + CRED- (belief) + -OUS (full of)
incredulity means disbelief; doubt
“It is always well to accept your own shortcomings with candor but to regard those of your friends with polite incredulity.” —Russell Lynes