https://www.youtube.com/watch?v=v_EIMiGnWUA&lc=UgxukngFH-CcUVp5Ard4AaABAgWhen I rebuked a different rabbi, some people complained that Noahides shouldn't do so.
As explained in The Divine Code, it is an obligation to rebuke a person for sinning in matters that are forbidden by the Noahide Code, if that could convince him to stop. This follows from the Noahide commandment for Gentiles to establish a just and correct society.
This applies whether the sinner is of the same, greater, or lesser stature than the person who gives the rebuke.