Analogous to opening a can of whoop ass. A dangerous substance, usually found packaged inside cans. When released, can cause a major sass attack to the person it is intended for, and is often used as a weapon of sass. More often the user warns the recipiant of an imminent opening of a can, if the recipient does not act as desired by the opener.
Person 1: "Man you sassed Ms. Shaniqua hard today"
Person 2: "Yeah i opened a can of whoop sass on her ass today"