Tell him to get a job and stay the fvck out of your business. Maybe back when he remembers everyone had horse buggies....that might be why he thinks she's speeding.
For fighting a ticket, bring up the point that there could be other cars matching your fiance's make and model and color on your street. It could happen. If you REALLY have a problem with the guy, confront him and ask him why he's upset. Be VERY nice to him....don't get angry. It will only fuel whatever hatred he has more. If he gets upset with you while you're all calm, see if he threatens you or makes any kind of move that you could sue him in civil court for. Talk to a lawyer about the situation and threaten this guy with a lawsuit if you have enough reason.