Why are things gender bound

Why do items have to be this or that, like things belong to either a boy or girl for example. Girls wear makeup and guys body build. These being stereotypes in my opinion and them things can be done by either gender. Some may find it strange that a girl is body building or a guy wearing makeup. But stop and think, if you comfy doing something, would you stop if someone didn't like it. 

Another point, clothing, why is this girls and that's guys clothing. I know that the clothes are made to it the figure of that gender but what if a guy has a rather feminine figure and likes to wear female t-shirts, jeans even leggings or tights. Yes it would probably look a bit strange at first but in the end is it really any different? A girl can wear a guys t-shirt and no one would really see any different, how ever a guy wearing a girls t-shirt might be more noticeable. And why clothing branded as male or female when it is clear that both gender can wear them?

The point I want to try and get across is that you should wear what you want. If you are a a guy and like female clothing, go ahead and wear what you find comfy, if you are a girl and like males clothing go ahead and wear guys clothes. For the people who bully you because of it, they are just jealous because you being different and being yourself, which you are allowed to do.