By "your culture", I can only assume you mean pubescent boys. It's an ableist slur in any culture that includes disabled people, whether you want to recognize that or not.
U do realise im a certified retard myself. What ur claiming is akin to saying a black man cant say the n word cos other black people exist in his culture.
No, what you are saying is that black people cannot be racially offensive to other black people. What is to stop you from saying something ableist? Clearly, nothing.
In your culture perhaps, but do you know the culture of the one who reads it?
Did that ever occurred to you that we are on a global social media platform?