He's '(as) stubborn as a mule'. [=he's very/extremely stubborn]
She 'has a stubborn streak'. [=she is often stubborn]
She's wrong, but she's too 'stubborn' to admit it.
(..) All that science stuff,that comes from jesus. Sheldon,your mom made dinner. I'm not hungry! Oh,leonard,don't trouble yourself. He's stubborn. He may stay in there till the rapture. We so sure that's a bad thing? I tell you,I love the boy to death,but he has been difficult (..)2007 TvShow: The Big Bang Theory Title: The Luminous Fish Effect Season: 1 Episode 4