Sometimes that IS needed.
I had a problem with a particular bully, that was a huge guy, but sucked in a fight, after being defeated multiple times in "fair" fights, he still kept bulling us.
So one day, I hit him inside the classroom with a chair.
This immediately stopped bullying inside the classroom, but he still kept bullying me elsewhere.
So during a field trip one day, when he started bulling me, I punched him in the ear, he grew furious and started to threathen me, so I pulled a switchblade from my pocket, and showed to him, and I was pissed off enough to do that with "honesty" (ie: it wasn't a bluff, I actually was in the mood to stab him if he continued his behaviour).
He never bullied me again. (teachers wisely put us away from each other though... and other students didn't even noticed what happened, none of the other students saw I was carrying a blade with me).
Eventually he got expelled from the school though, for other stunts he did (like showing for class at 7:00 in the morning already super drunk, and vomiting so much that you could figure what he drunk by looking at it and the smell... it was vodka mixed with Coca-Cola)
Also, once a kid kept stealing my sister stuff, and once threw my sister into some construction materials.
My sister one day took with her the ball of her mouse (remember those?), and when the kid stole her food, she waited the kid to turn around, and then promptly launched the ball against the back of his neck, knocking him immediately to the ground.
Also worked wonders, never the kid bullied my sister again.
EDIT: explaining the "bullying us" in my first phrase: in school there was several kids that went to Kung Fu school, they invited me and I joined too. The bully had the bad decision of choosing us (kung fu students) as his target, maybe unaware of that fact, thus he kept attacking us, and kept getting defeated (for example once he picked on the smallest guy of us, the guy weighed so little that he couldn't participate in kung fu competitions because he was 15kg too light for the lightest category... he defeated the bully with a continuous flurry of kicks that left the bully white t-shirt with several muddy shoeprints... the bully actually kept fighting, and another bully had to physically drag him away from the fight, otherwise he would kept advancing and getting kicked until he was seriously hurt)