why wasnt George happy at all with lenny and candy being in crooks room

Lenny could easily say something to get himself into trouble. He also would give away the news about the farm.

He wasn't happy because they weren't supposed to be in a "black" man's room.

In a second George stood framed in the door, and he looked

disapprovingly about. "What you doin' in Crooks' room? You hadn't

ought to be here."

Crooks nodded. "I tol' 'em, but they come in anyways."

"Well, why'n't you kick 'em out?"

"I di'n't care much," said Crooks. "Lennie's a nice fella."

I don't think it was specifically a "black man's room". George was paranoid period of Lennie venturing out of the barn or bunkhouse. Just my take!