Ignore. Turn away. Let it slide. Go along with it. Pretend it isn't happening. Feign ignorance. How is that GOOD by any standard? It is cowardly and is very close to being evil itself. Just my opinion. Another famous saying with which I do not agree. Wish I could but I don't.
"Bad men need nothing more to compass their ends than that good men should look on and do nothing".
John Stuart Mill. 1867.