there is no reason to be a jerk with the kid... Like some poster said, I love how when this topic shows up, everyone started to go to bjj classes to be muldial champs from day 1 and couldnt care less about fighting, its fucking bullshit.
Most people I know started bjj to learn how to fight, as a matter of fact, bjj has grown as fast as it did in the US and world because of the UFC, not because of guys wanting to be sport bjj players, so cut the bs...
To the kid (you are obvius a kid) yes bjj is awesome, you will learn how to choke people out pretty quickly and dont worry about killing anyone, its really really hard to choke someone to death (nor you will require to do it)
Getting in streetfights its stupid, you seem to live in a upper class neighborhood (since no one is jumping into fights) and just dont want to be push around, I understand that, having your ego crushed its horrible and can create permanent scars that could last your whole life, sometimes you gotta do the animal thing, so if it has to go down, so be it.
Oh and buy a gun is the most utterly ridiculous advice anyone can give out, are you going to shoot spoiled teens? yeah going to jail for your entire life because someone tried to punch you in the face seems like the logical thing to do....

gotta love macho men attitude...