what incident caused George to stop teasing Lennie and making him do silly things like walking off a cliff?

George tells Slim that he realised that it was not appropriate to tease Lennie any more when he almost loses his friend. George told Lennie to jump in a river. Lennie followed George's instruction because he trusted him. George was betraying that trust, and Lennie nearly drowned as a result-

'He damn near drowned before we could get him. An' he was so damn nice to me for pullin' him out. Clean forgot I told him to jump in.'

George realised that he was abusing their friendship and was not showing the loyalty to Lennie that Lennie showed him-

'Well, I ain't done nothing like that no more.'