What is this is what i do i sit on you?

The phrase "This is what I do; I sit on you" is ambiguous and could refer to many things, depending on context. To understand what it means, we need more information. It could be:

• A piece of furniture: A chair, a toilet seat, a cushion.
• A person or animal: A pet, a child, or even a person who is being domineering or controlling.
• An object's function: A lid, a stamp, a weight.
• A metaphorical description: A burden, a responsibility, a problem.

Without further details, it's impossible to give a specific answer. The statement is deliberately vague and open to interpretation.