to cap it all (off)

to cap it all (off)

An expression indicating the final item in a list of particularly positive or negative experiences or situations. What a bad day: I left my phone in the grocery store, my car broke down on the way home, and, to cap it all off, my groceries broke through the bag as I was walking to the front door. They really threw me a wonderful party. Costumes, games, and, to cap it all, my favorite kind of pie.
See also: all, cap