flea in one's ear, a

An annoying hint or a stinging rebuke, as in He has a flea in his ear about their relationship, or If he doesn't bring the right equipment, I'll put a flea in his ear. This expression originated in French and has been used in English since the 1400s.

The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.