drop the dime on

drop a dime

To snitch or inform on someone to a person of higher authority. Originally street slang for informing to police, it refers to the old price of using a public payphone (10 cents). Primarily heard in US, South Africa. Timmy is such a teacher's pet, always ready to drop a dime on any of the other students he thinks are misbehaving. He knew he was facing 10 years in prison, so he agreed to drop a dime or two to police in exchange for a lighter sentence.
See also: dime, drop
Farlex Dictionary of Idioms.

drop the (or a) dime on

inform on someone to the police. US informal
1990 Scott Turow The Burden of Proof Dixon says he's thought it over, the best course for him is just to drop the dime on John.
See also: dime, drop, on
Farlex Partner Idioms Dictionary
See also:
  • drop a dime
  • iceman
  • drop
  • drop someone
  • dropped
  • flag
  • flagged
  • flagging
  • squealer
  • hired gun