Maliciously wrong answers, which do something unexpected and harmful to the user, should be flag-worthy.
For example, if someone asked:
How do I change the permissions of a directory?
Then the following answer should be flag-worthy, because it does something unexpected and harmful:
rm -rf directory
By contrast, the following is incorrect (the command name is mis-spelt), but wouldn't be flag-worthy:
I recently flagged an answer as maliciously wrong, but was declined for doing so.
You just click on the red maximize button
The red button doesn't maximize a window, but closes it instead, which is unexpected and harmful behaviour.