The evil bit is a construct introduced as a joke in the realm of computer networks, but it doesn't mean that the idea cannot be recycled and applied elsewhere. I will explain how it can be used in the context of human relationships.
You can refer to Wikipedia to understand what the evil bit is, or rely the following "plain English" explanation.
[Declaring] the evil bit is the act of making your harmful intention public. If the evil bit is enabled, it means that you're plotting something bad.



