Give someone the cold shoulder
To be unfriendly to someone and ignore them deliberately.
This idiom originated in the early 1800s. It is said that welcome visitors to a house were served a hot meal but someone who was not welcome was given a cold shoulder of whatever meat was being eaten. The shoulder was known to be the coldest and toughest part of the animal and a much inferior meal.
Give someone the cold shoulder
“I haven’t spoken to Susan for months. I’ve tried calling her a few times but she keeps giving me the cold shoulder. I don’t even know why.”

“I think you should stop giving Jeff the cold shoulder. I know he upset you but he’s really sorry and he wants to be your friend again.”

Paul: “Hi Jake. How are you feeling today?”
Jake: “Hi Paul. You’re the only person who has spoken to me today. Everyone else is giving me the cold shoulder.”
Paul: “Well I’m not surprised. You were very rude to everyone last night. Don’t you remember?”
Jake: “Oh no! I must have drunk too much – I don’t remember anything!”
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