I agree.
If they weren't flying over large gatherings of people (or had a parachute equipped) I probably wouldn't say anything, but since they're putting people in danger I'd report. If they're posting all these things on social media then it's...
Because you have negative feeling about this person, and you know that it would be a **** move if the only reason you were to report him was personal animus. However, this person is engaging in unsafe behavior that could put others at risk and...
If the Pilot is part 107 then Sorry but I would report them to the nearest Flight standards District office. If his work has not gotten him noticed already.