Most of us are a mix of both. We laugh, get excited, get cynical, exude irony and live with hope. We try to treat other people with respect and not get them down - though we may fail without meaning to.
Positive people are wonderful to be with. I have one friend who is extremely positive, which is the biggest reason I love hanging out with her when she's in town - though we barely keep in touch otherwise. Not that she doesn't have her bad days. But if I give her any bit of news about my life, she is always excited, optimistic and supportive. So when she was here, she was the first person I would usually talk to when I had something nice to share: just witnessing her exuberant response would make me feel even happier.
And there are some who are so effortlessly negative. Tell them you had a fantastic dinner last night and they will respond, "I bet you didn't cook it!" Have them over as a houseguest and the first thing you're likely to hear in the morning is "Good morning! So you're finally up!"
All of us do that kind of thing once in a while, especially with people we are close to enough to speak our minds. But for some, the negativity overshadows the rest, even though it doesn't seem to get them down. Maybe it's a sign of insecurity. Maybe "that is so out of fashion" translates to "I'm better dressed, even if she is better looking". I don't know.
I do know that I don't want such people in my life. And I'm glad that I don't have any, any more. If I want someone to criticize me, I have the Guy, thank you.