Continuity mistake: When Dave is shot by Mindy while training, there are two bullet holes in his jacket when he has only been shot once at that point.
Continuity mistake: When Mother Russia tears off the car door and uses it as a shield, she then throws the door at another police officer and there are no bullet holes/dents visible.
Continuity mistake: When Mother Russia destroys the police cars outside Night Bitch's house she goes from car number 5 to the group of bad guys outside the house in an instant.
Continuity mistake: Dave goes to the hospital to visit Night Bitch. He said "I'm Kick Ass", while removing his glasses with his left hand. In his right hand, he has flowers. When he sits on the bed he is instantly wearing his glasses again.
Continuity mistake: When Kick-Ass first enters Justice Forever headquarters, there is a jar of peanut butter on the shelf. During his close-up, the peanut butter jar has vanished.