How should I react to someone yelling at me for doing the right thing?

Ok. First things first I'm a Scorpio and I'm pretty sure this person is bipolar. I have a little cousin who rides his bike up and down two streets. Where there's thugs and nightly shooting and kidnapping. One day one of his caretakers was cooking breakfast and he left without telling her. Ok. So two days later (today) I talked to his grandpa. He stared yelling at me saying "YOU CAN't TELL ME HOW TO RAISE A CHILD! HE CAN COME OVER TO YOUR HOUSE IF HE WANTS TO! IT'S NOT DANGEROUS IF I DON'T SAY IT IS! And stuff like that. He called me "little girl" I FLIPPING HATE WHEN PEOPLE SAY THAT LIKE WHAT THE FLIP DO YOU THINK GIVES YOU THE RIGHT TO SAY THAT.Anyway I went to my room and played minecraft and he comes in looking for my cousin's clothes. Once again he called me little girl and told him not to play with him like that. At that point I wished my diamond sword was real. Now I'm outraged and basically punching my keyboard to type this. I can really see my vains now…