i actually managed to get a knife onto an airplane post 9-11.
i didn't do it intentionally. a couple years prior my brother had given me one of those "swiss army credit cards" for my birthday
and i kept it in my wallet.. flying from Boston to Miami, i walked through the metal detector, set it off, emptied my pockets into a tray, walked back through and they handed me the tray on the other side. didn't run the tray through the x-ray machine.. i didn't even realize what i had done until the trip home from Miami to Boston.. that time they sent the tray through and i got a LOT of attention VERY quickly.
i let them keep the card, inasmuch as it was breaking apart from years of riding in my wallet.. still...... kinda... um.. yeah..