When I was 18, my gynecologist's office apparently forgot to tell me to take extra strength ibuprofen before my cervical biopsy — that's the recommendation they use. I got the same 'just a pinch' spiel, and they decided it was worth it to just go ahead and do it anyway. (Surely, they had some ibuprofen they could've given me.) The sample the doc took got stuck, and he was yanking on it while it was still attached. The nurse who was with him had to grab and hold my leg because she saw I was about to kick him in the head.
I had done eight years of Tae Kwon Do at that point. I would have made an ass of myself. If doctors really think it doesn't hurt, perhaps they should just shut up and deal with however we choose to express our clearly fake pain.