We've learned some very deadly techniques and how to break people's bones, naturally those moves are illegal when it comes to sparring or competition.

I remember learning how to stop a Samurai from unsheathing his sword, crippling him and then ending his miserable life...can't see many real world applications, but it was a good way to practice the bunkai for the kata, Tekki Shodan.
In our style there's a huge emphasis on control, when we spar we have it so all moves are just about touching the opponent, one: to not injure them and two: to have complete control over your techniques, so if you do ever have to use them outside of the dojo you have much more control over the situation, rather than just running in and breaking every bone in the attacker's body.
Quote: "In karate we break boards to demonstrate speed and directness of the strikes energy. If your technique is slow the board will not break, if your energy is being directed all over the place it will not break, if your accuracy is crap you may break the fingers of the person holding it."
Also, wear gloves that cover the whole of your fist...that's how I got the scars on my knuckles.

Still, I broke through the board.
And of course martials are very much an art form, particularly with things like kata, I love doing them.

This was my grading kata:
I know there's flashier looking styles out there, but I love Shotokan because it's about technique and form rather than looking impressive.