So...it's defined, but it's impossible to know whether it's happening unless the person specifically tells you they're trolling? That sorta seems like a flawed definition.
Can you define lying? Has lying been defined? Check your dictionary.
Knowing what a lie is is not the same as knowing when someone is lying.
Oh it's been very objectively defined. Knowing when someone is trolling, or when they legitimately believe what they're saying is the problem.