Why are people so hurtful? :(?

I just played guitar in front of my class. It was with my friends, one who sings and plays piano, the other who plays bass. And after we played everyone was like wow good job (to the bass player) then they were like oh that sounded mean, you too (to the singer) and they just said nothing to me. They know I'm really shy and they have never heard me play. So they complemented the other two and I was right there, and they don't say anything. Why would they be so mean? :(