The plainclothes guy was performing his duties and had no expectation of privacy. The plainclothes guy pulled a gun on someone for no apparent reason while expecting privacy. The first scenario no harm no foul, not the best way to have handled it but the result was a ticket for the rider and no one was hurt. The second scenario the plainclothes guy goes to jail along with the rider both for separate offenses. The plainclothes guy loses his badge. I don't see how the police get to have the best of both worlds.