Flattening chicken breast halves serves two purposes: It provides more surface area to rub in the Greek-influenced seasoning, and it ensures that the chicken cooks quickly. 2006 July 19, “On The Fridge”, in Washington Post:
(transitive) Of butter, to mix in by rubbing.
(idiomatic, transitive) To make a point in an irritatingly emphatic manner.
Postcards from Florida might mean someone is rubbing in the fact he or she has been lounging on the white, sandy beaches 2003 March 9, Glenn Davis, “U.S. vs. Mexico a day of celebration, opportunity”, in Houston Chronicle: