1. What does it mean?
내로남불 shortens 내가 하면 로맨스, 남이 하면 불륜. Beyond the literal romance-and-affair contrast, it criticizes applying a favorable rule to oneself and a harsher one to someone else.
Also written or said as naeronambul
2. The nuance
It appears in everyday disputes as well as political arguments. A fair comparison still matters: different circumstances can justify different responses without necessarily being hypocrisy.
3. Examples
“남의 지각은 혼내면서 본인 지각은 괜찮다니 내로남불이지.”
Scolding others for lateness while excusing your own is a double standard.
“나도 같은 실수를 했다는 걸 알고 내로남불이었나 돌아봤어.”
Realizing I'd made the same mistake made me question my own double standard.
Sources
References support the meaning and usage. Example sentences are written for NoCapWiki.