Sounding the horn unnecessarily and whilst stationary is an offence , and also is a disturbance of the peace .My neighbour of twenty years ago took the view that the estate road , two cars wide, bordering his house boundaries on his side of the road was his domain. If anybody was parked there when he came home he'd sound his horn until somebody came out to move it. He virtually never parked on his drive and made it as difficult as he could for other residents. About a year before we moved we had a friendly discussion about his attitude and he never spoke to me again.
A phone call to the police would have been worthwhile .