troll

Generally annoying people on the internet, whose primary motivation is to
cause disruption, distress or anger. The name comes from the grumpy
and chaos-loving character from folklore and fantasy.

Trolls typically have no interest in the topic or thread under which they
are posting. The usual advice when encountering trolls is to ignore
and/or block them, but this is sometimes not an easy solution. When
unleashed within a forum, stream or mailing list trolls can quickly
cause enough dissarray to destroy communities which took years to build
and as such they should be recognized as an existential threat to
software projects if they're not quickly dealt with.

Hired trolls may also be used for political purposes by governments or
corporations to disrupt rival organisations and spread fear, uncertainty
and doubt.

Also see shitposting.