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.