a cop is a cop 24/7 and can act as such at any time, that being said, find out how to report him to internal affairs and or complain to his commanding officer. Every captain, lietenant, or chief I have ever met would be embarassed to have one of his officers ticket someone while off duty. Would probably get dropped just by talking to his commander, but should be dropped if you have to go to court.

what was he saying was wreckless that you did?

I know of a fhp trooper that was given a day without pay for writing a speeding ticket to an on duty in a marked car, sherrifs deputy, this kind of thing is bad PR for the department.