Continuity mistake: When JD opens the beer can with the "John Dorian three taps method" inside Dr. Cox's car, he holds it in the hand in different ways.
Continuity mistake: When JD gets hit by the blue paint and confetti by the Blue Man Group at their concert, most confetti in the next scene disappears and JD is almost covered only by paint.
Continuity mistake: When JD is trying to free his hand from the glass bottle beating it on the pole, his sleeve shirt is first lowered and then raised in two different shots.
Answer: No, it was a fake, they used a stamp.
It is real.