The old man is telling George and Lennie about Curley. Curley is the boss's son and he is a small guy who hates big guys and Lennie is, so the old man warns him about staying away if he doesn't want to get in a fight. George says he hates those kinds of people so he is mad and tells Lennie what to do in that situation. Here we see a conflict between a big guy and a small guy.
Here we see a conflict Lennie holds within himself. Lennie has a certain fetish to pet mouses. With a mental disability, he has a hard time to understand that he can't touch little girls because he says he wants to pet their dress like a mouse. This leads to having to escape town with george in order to not be killed.
On this scene we can visualize how the people stare Lennie. By his way of acting which is the effect of his disabilities. People stare and treat him differently. But as Lennie doesn't know he is disabled, he thinks he acts normal but he doesn't know he is disabled which makes him ask why people give him those stares.