Me and a friend used to tease this christian dude at school. He was really awkward, skinny and wore these geeky glasses. It's not like we tormented him or anything, it was mostly just us being us and him being him. We would often discuss heavy metal and satanism, and he would dislike it very much. At some point, we started bringing it up more if he was around. Eventually the novelty wore off and we departed on good terms.
I later met the dude when I realized we were serving in the same brigade during our military service. He was a logistics guy and I was an NCO, so we both ended up serving a full year. We occasionally stay in touch, though not that often.
That was me... teasing? I suppose it counts as mild bullying, not as hardcore as social isolation or straight out violence, which I've both experienced personally. From grades seven through nine I was essentially cast out and exiled from any and all social circles around the school. I actually didn't speak a word for the first year or so. During second year, most people heard me speak for the first time.
On the ninth grade, the situation took a rather comical turn. Now, I've always been big and strong, so I was never really physically bullied. But the out of the blue this little Kurd dude starts picking on me. He was half my size, and I never really had a chance to speak to him about his issues. He did these hit and run attacks on me. Spat in my face once, completely randomly. One time during P.E class, he took a running start and leap-kicked me in the back. I didn't even stumble, and before I knew it he had sprinted off. I still remember the look of confusion I shared with the guy standing next to me. He did this on and off for the whole year. He was perhaps most of all annoying, rather than a true menace.