It's a copy and pasted block of text usually posted on a message board to troll newer users and as an inside joke between older users. Copypasta can usually be found posted in a discussion about any subject, and
will usually be intended to draw out newer users into responding negatively to it, much to the amusement of more veteran users.
Copypasta might have started out as a real post somewhere, but
people might have found the story so stupid or amusing that they post the exact thing years later to mess with
people. It's much like a group of
friends getting together to mock what another person said in the past and laughing about it.
User 1 posting copypasta:
"Hey Faggots,
My name is John, and I hate every
single one of you. All of you are
fat,
retarded, no-lifes who spend every second of their day looking at stupid ass pictures"
User 2:
Hey, I'll kick your ass for talking like that
User 3:
"lol, look at this guy replying to copypasta"