According to Curley's wife , why are the men afraid to talk to her when there is more than one present ?

From the text:

She regarded them amusedly. "Funny thing," she said. "If I catch any one man, and he’s alone, I get along fine with him. But just let two of the guys get together an’ you won’t talk. Jus’ nothing but mad." She dropped her fingers and put her hands on her hips. "You’re all scared of each other, that’s what. Ever’ one of you’s scared the rest is goin’ to get something on you."