I'm A Terrible Mother

My son went with his father and bought this really silly cartoon network hat. Well, I'm a terrible mother and he wants to go live with his father because, I won't let him wear the hat to school. I just think it's a silly hat and I feel he needs to spend more time focusing on school and less time focusing on trying to be silly and different. The hat looks like something someone would buy for a two year old and I don't think a 11 year old boy should be wearing something like that. Since, he has changed the way he dresses his grades in school have dramatically dropped. He already wears all the crazy concert t-shirts and crazy sunglasses, I don't want him to turn out to be one of those kids with gauges in their ears or bar piercings in his eyebrows or lips. I believe a child should be able to express their individuality to a certain extent. I don't think there is anything wrong with the kids who put gauges in their ears or do the bar piercings. I just don't my son to do it. I don't think a teenager is old enough to make a decision like that. Gauges and piercings are permanent and I don't want him to make a decision he will regret later or interfere with his success of finding a job when he is an adult. What do you think?