1. What does it mean?
귀차니즘 combines 귀찮다, finding something bothersome, with the suffix-like sound of '-ism.' It playfully treats reluctance to do ordinary tasks as a whole philosophy.
Also written or said as 귀차니즘 발동
2. The nuance
Use it for a casual mood, especially your own. It is not a medical term, and labeling someone else's fatigue or difficulty as 귀차니즘 can be dismissive. The joke is about not feeling like doing something, not about whether the task matters.
3. Examples
“귀차니즘이 와서 저녁은 냉장고에 있는 걸로 먹었어.”
I couldn't be bothered to cook much, so I ate what was already in the fridge.
“운동복을 미리 꺼내 두면 아침 귀차니즘을 이기기 좀 쉬워.”
Putting out my workout clothes ahead of time makes it easier to beat that morning can't-be-bothered feeling.
Sources
KoreanClass101: Korean language lessons
References support the meaning and usage. Example sentences are written for NoCapWiki.