what does Charlie mean when he says, “I felt naked

The guys put something in Charlie's soda at the party because he didn't want to drink. Then they encouraged him to dance with Ellen, all the while sticking out their feet to trip him..... to make fun of him. Charlie felt naked because of the way everyone was staring at him and laughing. He ran from the party and proceeded to be sick.

He felt naked because of the way everyone was looking at him.