With a flea in your ear British phrase informal
A harsh reproof or rebuke
I'll be sure to put a flea in your ear, if you keep repeating the same mistake.
If that kid cries one more time, I'll send him back to his parents with a flea in his ear.
My mother gave me a flea in my ear over my eating habits.
Used to describe someone who is naive, gullible, inexperienced, easily fooled, ignorant, unsophisticated, etc.
A severe criticism or rebuke that's used to dismiss someone
If you cover your back, you foresee you being accused of or blamed for bad consequences and do something to avoid that.
To provide the police or authorities with information to expose someone’s wrongdoings
The phrase first appeared in 1426 in John Lydgate’s The Pilgrimage of the Life of the Manhood, which was a translation of a work by the French Cistercian monk, Guillaume de Deguileville. Deguilville used it to denote the spiritual emotion that is evoked by beholding great wonders. And in more modern times the French use their version of the expression to denote having doubts about someone. However, English speakers tended to concentrate on the physical discomforts that having a flea in your ear can cause and have used it in that figurative sense through the centuries.