Have a cow
Definition 1 of 1
Pro Tip 1/3Emotional Intensity
This phrase is used to express strong emotions, like panic or anger, in a hyperbolic way. 
I'm going to have a cow if I can't find my passport before the flight!
Pro Tip 2/3Informal Speech
Used mainly in casual conversation, not suitable for formal contexts. 
Just relax, don't have a cow over this little issue.
Pro Tip 3/3American Slang
Popular in the United States; English speakers from other regions might be unfamiliar with it. 
My American friend told me not to have a cow when I got stressed.