Have a corncob up (one's) ass American vulgar slang
Used to describe someone who is extremely rigid or inflexible in their posture or demeanor
She was so nervous that she had a corncob up her ass.
I know he has a real corncob up his ass from the way he speaks.
Used to describe someone who is extremely rigid or inflexible in their opinions or beliefs
She has a real corncob up her ass when it comes to her emotional and sexual life.
Used to describe someone who is irritable, unfriendly, or humorless
James must have had a corncob up your ass or something when his friend played a trick on him.
The verb "have" should be conjugated according to its tense.
It was often said by a photographer when he would like small children to look at the camera and smile before he took a photo.
When the photographer said “watch the birdie”, all of us looked at the camera and smiled.