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.