1) Post a picture of a group of people, suggesting it contains both you and your intended victim.
2) Leave an accompanying story about how this "newfag" wants to join a /b/ group that you and your oldfag friends set up at school.
3) Say that he failed your meme admission test ("He didn't even know Longcat!!1!")
4) Post a random phone number, followed by the standard "inb4 not your personal army", "let's teach this newfag not to mess with anonymous" crap.
5) Bump the thread 5 minutes later pretending you know the OP, then drop the real number and say it's his. You get twice the rage