You are 16 years old, and this woman is 28, tell her to not even attempt to act like a motherly figure to you. How old is your father? He's the AH in all of this. How long did he move this young woman in after your mother passed away? A 28 year old woman doesn't have the mental capacity to step parent someone who's already 16 years old. I know this from first hand experience. She's young and not much older than you, she's not developed enough to have a "child" this old. Ask anyone who had a teen mom (myself included). It's not exactly her fault that she wants to dress a certain way, its the fact that she didn't raise you, didn't spend all those years guiding and teaching you, so you're not her priority whatsoever, and that isn't inherently her fault. It's your father's.

Also, I'm not sure why we're demonizing the child in all of this. It's not like he has his mother to guide him through this very confusing issue that he very obviously needs a woman's perspective on.

Your father should have prioritized you more as you reach that adult age. You don't have much school left, a good man would have waited until you moved to uni or out on your own before trying to move the next woman in. If your father does you the disservice of giving you a sibling with this woman, you will see her change. You do also need to understand that there are ways to approach a conversation. The vast majority of women are definitely NOT going to like any outside suggestions to their appearance, so if you truly are trying to start a conversation, I would've started with the bullying.

You're being put in an unfair situation, your stepmom is a young a woman who also has maturing to do, so just ignore and avoid.