Is there a Russian equivalent to "Don't have a cow"? Obviously when we say to someone "Don't have a cow" we aren't asking them not to give birth to a calf, it's just a colorful way of asking the person not to over-react, get angry, or yell. Similarly, we might say, "He's going to have a fit when he finds out" or "He's going to go postal when he finds out" or "He'll blow a fuse when he finds out" or maybe "He'll get his panties in a bunch when he finds out." There must be some fun idioms in Russian to cover expressions like this.