Why do some people always feel the need to be negative with others?

my aunt is that kind of person. yesterday i drove her around town so she can do her shopping. my boyfriend was in the car with us. on our way back home he drove my car and made a wrong turn.i felt that she didn't like it then she started criticizing his driving in our language. saying he wanted to drive so good that he messed up. i was like ok so i told him gently that he should take his time to learn since he's a new driver. this morning she calls me twice. the first time she tells me he's a bad driver i shouldn't give him my car for my safety not only hers, that he should practice with someone else car then she adds that he was musty had a bad odor that she had to spray perfume on herself in the car. like i was in the car i didn't notice all that. i didn't see her doing it.telling me to buy cologne for him. then say she's going to call me back. when she called i didn't pick up.so she called the house phone and told them that she's been calling me 3 times and i didn't pick up when she only called once. so i get on the phone with her she repeat what she said on the first call then she tells me i don't have a good boyfriend, tells me to keep looking for someone better than him because he's not the right one, he's childish, immature, he's clumsy. i can have him but i can still look for a better one, more mature for me.i'm like wow.then she tells it to everybody in the family. i know he's a little immature but we're young and people change.besides everyone isn't perfect