You can neither prove nor disprove that we are in a simulation, just as you can neither prove nor disprove the existence of God. In both cases, you cannot come up with a measurable experiment, your claim is not falsifiable, so you cannot use the scientific method to prove or disprove it, and the discussion will inevitably lead to an argument about semantics: "how do you define simulation", "how do you define god", "how do you define define", etc.

Almost all similar arguments I witnessed ended in an argument about semantics, where one came up with his own definition of a term and tried to prove or disprove it, instead of focusing on a commonly accepted definitions agreed by both parties.