why was the boss mad at george and lennie?
In chapter 2 of John Steinbeck's Of Mice and Men, we witness the arrival of George and Lennie to the ranch. As previously seen, George and Lennie have had considerable obstacles leaving their previous town on account of Lennie's limited cognitive abilities, which result in his getting into trouble for causing accidents from which they have to escape later.
When they finally arrive, the first person who tells them about the boss being angry at them is Candy, the custodian of the ranch. He tells George that the boss was expecting them the night before, and not later. However, Candy also says that the boss is a "pretty nice fella".
This is also the part of the story when George and Lennie have their first encounter with Curley shortly thereafter, and the moment when Curley notices George's speaking on behalf of Lennie every time Curley asks a question. Immediately, there was a bad rapport between the boss and the men which will last until the very end of the story.