Raise a grievance if the damage isn't made good and Mr Tw*t promises never to do anything like that again, it is grossly unprofessional. I like the grease idea as revenge but I'd play with his head to make him think of the consequences. I'd have got your dad to ring the manager up 10 minutes before your bro got to work the next day asking if anyone had seen him as they'd just checked his room, realised he'd not come home last night and there'd been a news report of a young lad in critical condition after getting knocked down crossing the road not far from where he works.