1. What does it mean?
집돌이 is the male counterpart of 집순이: a casual nickname for a homebody who enjoys resting or doing hobbies at home. It says something about preferred downtime, not a person's entire social life.
Also written or said as jipdori
2. The nuance
It can be affectionate or teasing. Avoid using it to diagnose social anxiety, criticize a person's lifestyle, or assume they never want an invitation.
3. Examples
“형은 집돌이라 집에서 요리하는 주말을 좋아해.”
My older brother's a homebody who likes weekends spent cooking at home.
“집돌이 둘이 만나서 실내 게임만 했어.”
Two homebodies got together and spent the time playing indoor games.
Sources
References support the meaning and usage. Example sentences are written for NoCapWiki.