Took off with the parking brake set at 50% - Only second time on grass, so the reason for the slow roll was obvious!
Good job I realised it in the air.
Pulled up into my "parking" spot (more like a hill). As I cut the engine and removed the keys I dropped my pen. Bent down to pick it up, bought my head up and realised the plane was rolling down towards a nice new Archer! Missed it by whiskers. - Yep, that parking brake again.