1. Pranks cross the line into bullying when the person who is being pranked can't just shake it off afterwords. Once someone starts being hurt by it then it is bullying. Up until that point it's just harmless fun.
3. Once upon a time, I was just a small boy looking to play some football. As I trotted onto the field a big hairy man approached coughAdamBrobstcough. He ran up to me and slapped me in the face. He then proceeded to grab me and tapped me to the field goal post. He then began throwing footballs at my face, boy does he have a strong arm.
2. Intention doesn't really matter because just because you weren't trying to offend someone doesn't mean you didn't. The reaction is all that really matters because that's what you take away from the situation. Intentions don't always lead to the reaction you wanted. Don't be a bully, don't be like Adam.