What does it mean when a guy says I look mean?

I was sitting with my guy friends and we were talking about each other's first impressions. One of my friends said they thought I was a bitch and unapproachable and only talked to me because I was with his friends. He then said he would of never talked to me if there others were never there. Then my other friends said that they also thought I was mean before they met me. (I always smile when I'm with friends). Why would they think i'm mean on their first impression?
What does it mean when a guy says I look mean?
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