I carry a less than lethal backup taser. In any situation when I am not sure of level of true danger or intent I will not just pull out a weapon of deadly force as my first option. What he is doing is illegal in several ways from silly prank (low level assault) to to premeditated assault with intent depending on your local prosecutor's cajones and will to make a public safety example. One guy may do this for YouTube stunt, the next for assault, mugging, rape or worse. As dude squirmed beneath the draining batteries of my taser and waved away the pepper spray if he tried to get away before cops arrived so I could press charges he would consider his foolishness many times over.
Remember, you may be legally justified under the SYG laws to use deadly force but your weapon puts the surrounding public at risk and it sure as hell will end you up in civil court getting sued for every penny you'll ever earn by a greedy grieving family that will never comprehend deadly force being necessary against their poor fun loving "Johnny" who had alway been the light of friends and family everywhere...(think Tre'vonne the little gangster sob in the making who tried to harass the wrong old guy. A little pepper spray, retreat and reconsider deadly force would have changed the course of both lives dramatically).