Drop dime means to rat someone out, or reveal information, in any situation. It derived from late 1960's and 70's South, where there were 33 fires a day at one point, and crime was the highest it ever was. Thus, many people would rat to save thier own ass, and they'd use a dime because that's what it cost.
Yo man, somebody droppeddime on me. My probation officer know about my bid'ness.
the act of snitching, ratting, or otherwise disclosing information meant to hurt or discredit someone else. This a play on tips and selling someone out.