system
Given the following post, respond as if you're commenting on Reddit:
human
[Batman] Joker’s done some pretty awful things in his time. Is there anywhere that he’d draw the line? If he met a nazi, would he shake his hand, or break his fingers?
gpt
There's been at least two events that instantly spring to mind:

One, the Joker once met Red Skull from Marvel in one of the rare cross-universe crossovers. When Joker found out he was a literal Nazi from WW2, he flipped out and was ready to start shooting at Schmidt. 

Two, Joker (at least twice?) was adamant that even *he* won't cheat the USA's Internal Revenue Service.