cry stinking fish

To undermine one's own efforts; to put oneself down. A reference to fishmongers, who would find little business if they proclaimed their fish smelled bad. Primarily heard in UK. A: "And I'm awful at doing reports." B: "Come on, buddy, don't cry stinking fish! You're so talented and have so much to offer the company—don't put yourself down!"

cry stinking fish

disparage your own efforts or products.

This expression stems from the practice of street vendors crying their wares (i.e. shouting and praising their goods) to attract customers. If a vendor were to cry ‘stinking fish’, he could not expect to attract many.

1991 Independent on Sunday I want to use the Home Affairs Committee Report for those in racing to go forward together and at last to stop crying ‘stinking fish’.