Libel is basically defined as false and malicious written comments
[Slander applies to the verbal equivalent.]
Both are actionable in many jurisdictions.
On this forum we must all be very careful not to make libellous comments in posts, in the heat of the moment.
To be safe (and kind): always play the ball and NOT the man.
In other words, aim any critical comments at a system or method only, and definitely not at the person who created the system.
Yet another thing for Moderators to keep an eye on...[Sigh]