Getting laughed at by an entire classroom of teenagers

So I work as an office aide for one of my school's secretaries, yesterday I was asked to retrieve a kid for something (I don't know what, more than likely truancy or absences.) When I entered the classroom, EVERYONE seemed to immediately burst out laughing as soon as I entered, two girls were even looking at me while snickering behind their hands, and the teacher of course did jackshit to reprimand them at all because the staff at my high school are as useless and spineless as wet tissue. I wasn't wearing anything weird, in fact, I actually thought I looked pretty good that day, but unfortunately due to my fucked genes, I'm severely balding to the point that I look more like forty than eighteen, and the dickheads at school always seem to love to point that out to me, as if I don't hate myself for it already. Plus I'm overweight, not obese but noticeable, how do I deal with situations like that?