What to do if i have a unfair teacher?

In my school there this science teacher which only picks on certain people such as me because this other day i had this incident where i knocked my head of the table and said bull**** and all of the sudden i got sent out and recieved 3 days of 1 hour detentions which is not a normal thing to do, normally i would recieve a telling of and sometimes they dont care. Me personally i do not misbehave during the class but there are other student which will argue,swear AT THE TEACHER which will only result the teacher laughing along or blaming the whole class for their doings and she treats with respect and does not give them detention AT ALL because she is scared of them or something.I know it is hard to understand but i dont know what i should do.