A bullys' gun is their mouth, their bullets are the cruel words they speak, their targets are those who they see as weak.
What can you do? Well for some the most tempting thing would be to throw a punch to shut them up, or instead find yourself your pride and strength, learn to ignore the words they speak.
Option 1 is more tempting but gets you into trouble, option 2 means you may known their inflated egos and burst their bubble, because when you stop reacting to the words they speak, they may realise you aren't the one who's weak.
A bullys gun is their mouth, their bullets are the words they speak, their targets are those they see as weak. So don't listen, don't doubt yourself, ignore the tempting urge to reply or lash out, they can keep firing but the bullets will soon rebound, the control, the power they once had will never be refound.