My 11 year old nephew is a sedistic @hole?

he doesnt listen to his MOM EVER !! he comes & goes and he pleases cussees her out etc.. He had a troubled past. my problem is i have a new baby and we have a very peaceful existance. we went to a family get togheter today he was there. he had a snake in a cage and i am DEATHLY afraid of snakes , he started chasing me around the yard with it it was horrifying. i was screaming at the top of my lungs, i thought i was going to die, my baby is traumatized now becuase it scared her so bad. he would NOT STOP. his mom came out and yelled at him to stop, he doesnt listen to her so he kept going. he saw the horror on my face and has some sort of sedistic streak becuase it only made him do it more. i used to lov ehim now i hate him and & i do not want me or my baby around him ever agin. how do i deal with this i will be excluded from family get togheters or else will have to be in the same room with this very unstaqble & dangerous boy?