I would have to be a wire guy to do this well but test tonight show that it is possible to do and with a plastic gift card it could be deadly in the right hands.
I use these for my tactical business cards: Probably the best tactical business card out there, but still a bitch to mount the picatinny rail
On a serious note throwing cards is great for hand eye coordination and can also help your aim with other objects. A small stack of steel cards could be quite deadly. I have to admit though that throwing a credit card has caused by far the most damage I've ever incurred.
There was a kid on one of the daily talk shows (Steve Harvey) that threw regular playing cards and stuck them into a watermelon, cut pieces of celery and zucchini, and even taught the host to throw and stick them into styrofoam. Awesome! Extraordinary Kids: Card Throwers Kajun
I don't know man,I just saw my first little twerp today with one of those triangular spinney things, Useless looking dude!