Only safe if the engine is cold. Keep in mind redline is just suggested. Don't let corporations and supposed engineers tell you what to do with your car.
Get a new friend. He obviously doesn't care about your property.
OP, are you serious??? First off, your friend is a dickhead and must be jealous of your car so he was purposely trying to harm it. Second, why the hell would you even let him do that to your own car?