Go on to any custom game and have at least one other person with you.
Have the other gamer run towards you while you run backwards away from them.
Throw any type of gernade on to the ground in front of the other gamer while he chases you (close enough to explode on to him when he runs over it, but far enough that it does not kill him).
When the gernade explodes, it will fling the gamer towards you and you will "punch" him and he will fly many, many yards.