Whenever I play darts with someone for the first time, I always like to scoop this prank up out of my standard bag o’ tricks: Wait until each of you have thrown a few turns and your friend is nice and relaxed. On the next round, after throwing your darts, walk up to the board, mark up your score, pull your darts out, and “accidentally” drop the last dart as you remove it from the board. As you bend over to pick up the fallen one, take one of the other darts, which still remains in your hand, and unscrew the metal tip so that only the wings and body remain. When you return to your prone position, turn and face your adversary with a huge grin and say “here, catch!” Cock your arm back and release the tip-less dart at a speed and rate that will not allow them to move out of the way.
Watch the disbelief in their face turn to a look of sheer panic as you cock your arm and they realize you are actually throwing a sharp, pointy, dart straight at their chest. If you do this quick enough, the only chance they have to protect themselves, is to block the dart with their arms before it hits their body or face. Some people shout profanities and others will squeal, rest assured; you will have a good laugh.