As I’m not 100% sure of this, I did some digging. In a much more recent ATMB thread it appears calling someone a liar is equivalent to insulting them.
I’m basing the above on this thread from last June.
As always, the Pit would be an exception.
ETA: Sorry, have to add. Avoid any question on the subject and just let the other poster know that they’re incorrect about what the posted and let them provide the proof to back it up.