Ok, this might seem rather lame, but he started it and somehow managed to piss me off a little.
Managed to cut off his sentence at some point, but you can't see that here.

You're now chatting with a random stranger. Say hi!
Stranger: hi
You: Hey
Stranger: asl
You: 18m
You: you?
Stranger: 18 in 2 days f
You: Happy birthday to you, might be a bit too soon, but anyway
You: What did you ask for your bd?
Stranger: thankyou
Stranger: your soo sweet
You: suckup
Stranger: not much
Stranger: hey that's not nice, I'mnot always a suck up. SUCK UP
Stranger: SUCK UP!!!
You: Ok ok
You: I believe you
Stranger: no literally suck up
You: Suck up what
Stranger: suck up ur own dick
You: I would if it fit into my mouth
Stranger: cuz now one else would
You: Your mother told me otherwise
Stranger: oh so it's big?
You: Not bigger than your anus
You: since it's been ravaged by your dad
Stranger: you do not no me
You: Of course not
You: You're so deformed you never go outside
Stranger: I am a model for your info
You: A model for retarded people's magazine
You: Why the fuck did you start this
Stranger: I am a sailor/surfer and I have tons of friends
You: Is this what you want
You: Sailor buttboy yes
You: Surfer because you like the sand in your vagina
You: Right
You: Fucking faggot
You: Pretending to be a girl
You: Who does that shit
Stranger: fuck you I hope you die and rot and hell and I bet it's puny
Your conversational partner has disconnected.

Scared him away