"RESPONSIBLE OF YOU"
This is used when referring to a specific responsible action that you took; an action that shows that you are a responsible person.
Example: If my son cleans up the mess that he made in his room, i can say:
"Cleaning up your room was very responsible of you".
Example: "If you spill your milk on the floor, it would be responsible of you to clean it up."
This implies that "you would be a responsible person" if you cleaned it up.