cock block ring

A device simple or extravagant that when placed on a woman's left ring finger effectively blocks her from accepting the advances of other men regardless of the qualities the other men possess.

Other names for this device are "promise ring" or "engagement ring"

Chris's friend Tim "Hey Chris I just saw your girl having dinner with another guy... I think you are in trouble because they looked damn good together!"

Chris "damn I better give her a cock block ring!"