The best example of how Steinbeck conveys the impression that George can easily get annoyed with Lennie is to be found in Chapter One, when the two men are getting ready to eat their last three cans of beans.
"There's enough beans for four men," George said.
Lennie watched him from over the fire. He said patiently, "I like 'em with ketchup."
"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...."
Then George continues for a full page with the complaints and recriminations that have been building up ever since the Weed incident and have "exploded" because Lennie observed that he likes beans with ketchup. George is feeling that Lennie is too much of a burden for him to carry. If he were alone his life would be easy. But, he complains, Lennie keeps getting him into trouble. In Weed they had to run for their lives because Lennie had molested a girl and frightened her into thinking he was going to rape her (which is what might actually have happened if Lennie hadn't attracted a lynch mob by assaulting the girl in broad daylight on the main street of a very small town). Weed is about four hundred miles to the north of where George and Lennie are presently camping near Soledad, and the two men have been more or less on the run until now. George only knows what Lennie told him about the Weed incident, and Lennie (1) does not understand his own feelings, and (2) lies to George consistently. George describes a small part of the incident:
He took on the elaborate manner of little girls when they are mimicking one another. "Jus' wanted to feel that girl's dress--jus' wanted to pet it like it was a mouse-- Well, how the hell did she know you jus' wanted to feel her dress? She jerks back and you hold on like it was a mouse. She yells and we got to hide in a irrigation ditch all day with guys lookin' for us, and we got to sneak out in the dark and get outta the country. All the time somethin' like that--all the time."
When George finally kills Lennie at the same campsite in the last chapter, it will not be entirely an act of compassion. George would really like to free himself from Lennie. The big retarded man is becoming too much for him to handle. In Chapter One when George tries to take the dead mouse away, Lennie puts up a strong resistance. He is beginning to realize that he has a will of his own and doesn't have to do whatever George tells him. George's display of anger is extremely significant. It shows that he is in fact continually annoyed by this feeble-minded giant and foreshadows the so-called "mercy killing" which will end the story. George's outburst also foreshadows the trouble that Lennie will get into with Curley's wife at the ranch.
In Chapter Two, after their interview with the boss, George expresses his annoyance again.
"So you wasn't gonna say a word. You was gonna leave your big flapper shut and leave me do the talkin'. Damn near lost us the job....Yeah, you forgot. You always forget, an' I got to talk you out of it....Now he's got his eye on us. Now we got to be careful and not make no slips. You keep your big flapper shut after this."
They would be in desperate straits if they lost that job. They are broke and have eaten the last of their food. George certainly has good cause to be annoyed.