George is upset with Lennie for various reasons. One reason for George's frustration is due to the fact that George and Lennie are on the run. They had to flee a town called Weed. Lennie frightened a young girl and caused George and Lennie to have to flee for safety. George expresses his frustration:
“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.”
George is extremely frustrated with Lennie. Lennie is always causing a disturbance of their peace. George is frustrated.
Another reason for George's frustration is the fact that Lennie has a dead mouse in his pocket. Lennie is too strong for his own good. He pets the mouse and kills it. George becomes frustrated with Lennie. He insists that Lennie hand over the dead mouse. Lennie does not want to release the dead mouse. George has to express his frustration in such a manner until Lennie hands over the dead mouse. Lennie in his childlike mentality is always frustrating George to the point of anger.
Next, George is upset with Lennie because Lennie desires ketchup with his beans. George expresses frustration because he can't seem to please Lennie:
“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 . . . An’ whatta I got,” George went on furiously. “I got you!”
No doubt, George does feel frustrated at having to care for someone like Lennie. Lennie has such childlike capabilities until he is always getting in trouble. This causes problems for George. He feels responsible for Lennie. He carries the burden of taking care of Lennie. George is frustrated with Lennie. If only he didn't have to care for Lennie, George's life would be easier. Still, George realizes that Lennie depends on him. He knows that his life would be even lonelier without Lennie. Also, he promised Lennie's aunt that he would take care of Lennie.
Even though George gets frustrated with Lennie, he always calms down and shows Lennie that he cares:
Because they have a relationship based on genuine affection, Lennie is willing to tolerate George’s abuses and George is willing to suffer the frustrations and inconveniences of taking care of a childlike Lennie.