A moderator or longtime trusted user on a community pretends to be a troll for April Fool's or something similar.
Trolly is so over the top or so cliched that he becomes Self-Parody.
In-Universe, Internet trolls show up in Real Life in the universe acting the same way they do on the internet.
Zig Zagged: ???
The community or place is something of actual interest to Trolly or the people are his friends. While he trolls elsewhere (and may eventually there given the motivation) he behaves and is a sincere contributor and/or a real friend there.
The place consists of trolls trolling trolls trolling trolls.
It is an Image Board or comment section where trolling is accepted behavior
Trolly and possibly others have decided that somewhere or someone is so deserving of an attack, for whatever reason, that they must troll there.
Lampshaded: "Don't feed the troll" and similar messages, flagging a post as being a troll and suggesting it be ignored to deprive the troll of attention.
Trolly makes his first post.
Someone questions whether that new user is a troll.
In-Universe, someone mentions that someone is a troll or that they got some bad comments/posts.
Trolly decides not to troll.
The mods and admins have strict rules against trolling and ban any trolls on sight.
"I think that guy that just logged in as Trolly Mc Lulz is up to no good."
Trolly discussing plans to troll somewhere.
An article or other commentary analyzing trolling and/or giving means to engage in it or combat it.
Conversed: "Did anyone remember that time Trolly Mc Lulz hacked the board to redirect to Goatse?" "I did, I was the admin on staff at the time."
People realize that Trolly has nothing useful to contribute and is simply using them for his own amusement or attacking them.
This realization, along with some truly heinouseventsFor the Evulz (see Played for Drama below) that escalates over time, caused people to think that Trolly is a Complete Monster. Add up with how Trolly never realizes that this is going to bring trouble and keeps doing it to be amused, the people banded up, hunted down and killed Trolly before he could spread further misery. When called out for murder, the people claimed that Trolly crossed the line that they would take that dirtied hand for a better future.