Very common message posted to messageboards.
Normally posted by a disgruntled user when upset and wanting attention.
While someone who posts such a message will sometimes
mean it and will never again go to that board after posting such a message, usually once they calm down, they'll come back and will be posting as though they
never posted it.
On some messageboards, such messages are so common and/or posted by certain users so much that
people have learned to automatically ignore them.
I logged in this morning to find yet another I'm leaving the board forever message. The
guy that posted it has already posted ten of them and returned less then twenty
four hours after each
time.