To jump on someone, then act like you're having a spazz attack. It's often used to humiliate and freak out the victim, or as a feat of bravery to show friends.
However, as you are clinging onto someone, only your lower torso and legs are free, resulting in a rather explicit-looking spazz attack.
Often used on short, weak, geeky people who are less likely to retaliate.

When you eat dirt for the first time and leave your family to build a shack in the woods