I make fun of people who cut and intentionally harm themselves.
That's so cruel! Why would you do that to people who are already clearly upset?
I'm allowed to because I also cut myself.
It sounds like you're projecting your own problems onto them, which you shouldn't do.  Get some help rather than make fun of the situation!
I'm ok with it, and I'm proud of who I am.
Just because you're comfortable with who you are doesn't mean everyone else feels comfortable with themselves. Self-harm is a serious issue and something people don't like to admit to. Making fun of someone who does it will just make them feel worse.