how does the author convey the idea that George is in a bad mood?

George is in a bad mood many times during the story. Usually this happens when he frustrated with Lennie. We see this in the beginning of the book,

"Well, we ain’t got any," George exploded. Whatever we ain’t got, that’s what you want. God a’mighty, if I was alone I could live so easy. I could go get a job an’ work, an’ no trouble. No mess at all, and when the end of the month come I could take my fifty bucks and go into town and get whatever I want. Why, I could stay in a cathouse...... An’ whatta I got," George went on furiously. "I got you! You can’t keep a job and you lose me ever’ job I get. Jus’ keep me shovin’ all over the country all the time."

George's rant is out of frustration more than anger. He is left in charge of grown man with the emotional and intellectual capabilities of a six year old. This, however, at the end makes it all the more touching when George says to Lennie, "I ain't never been mad".