I am familiar with the rules\laws for lazy runners, but I want to question the actions of the attacking team if the scrum half deliberately passes a ball into a retreating lazy runner who has his hands up signalling that he knows he is offside.
I am not saying that he was making a pass and the ball hit a lazy runner; what I’m saying is that he picked up the wall and post it directly into the lazy river and there was no one in line of the boss so he deliberately, almost cynically, threw the ball at a player and then shouted “lazy runner”
Technically the lazy runner is offside and interfering with play and this will result in a penalty. The fact that the lazy runner puts his hands in the air just highlights the fact that he is offside.
The simple answer is that if the lazy runner is not in the vicinity of the scrum half this can't happen, so don't put yourself in a position where the opposition can take advantage of you being offside.
However The Rugby Ref would be talking to the scrum half about appealing and not trying to "buy a penalty".
The Rugby Ref