I saw a guy stay with cards totaling 16 exposed, plus his two face down cards. Dealer was paying 18 and flipped over the guys cards- an Ace and a ten. He had hit a BJ, then busted and decided he'd try and bluff the dealer.
He said he thought a BJ was only black Ace and black jack. He thought the seven gave him soft 18 so the only card he could bust on was a ten or a nine so he took a hit.
After being yelled at and told not to try bluffing, he did it again a few hands later. He also counted with his fingers.