Had a can of diet coke like that a while back. Used a pocket knife. When the tab finally flipped up, the tab bent in half and was L shaped, and the tab on the can never even budged. We whacked the tab with the point of the screwdriver a few times and determined that whatever scoring process they use for making those tabs was done incorrectly on this one. Ended up opening it with a can opener (like the type you'd use to open a can of beans or corn or something), and just pouring it into a glass. It was weird.