OMG!!!
I laughed so hard my face and throat hurt and my eyes are watering.
A few to add to next list:
Create a guild named (insert name of one of top guilds)_sux.
Create a noob then propose to every high lvl in market (works with same *** too).
Use the following website to insult people in their native languages:

(or a similar website)
Fill inventory with staunchers and try to trade them to everyone (especially in middle of spawns).
Make and archer and lvl high enough for fly, wait for xp skill then go sit on item and fly so you can't be attacked (doesn't work if person can use magic attack).
Whisper everyone and ask where the bathroom is.
Whisper people and say something in a made up language.
Type only in 133t.
Speak only in pig latin.
Pig Latin - Wikipedia, the free encyclopedia
Create a (nude) lvl 1 red name and go hang out in ac and spam: you can't kill me, you can't kill me, you can't kill me, etc (I personally like saying: Neener, neener, neener you can't kill me!)
Make lvl 1 char and spam (in market): trade this account for 100 dbs!
Trade spam in jail/guild war.
Kill your guild members when they are attacking the pole/gate.
Make an archer and get it's lvl only high enough for scatter then take to towns and scatter everyone when next to guards (guard should kill you before you kill anyone).
Attack flashers.
Accuse all top players on your server of being botters/hackers/scammers on message board.
This takes a lot of work: Propose to people in tg.
Spam propose someone that's already married.
Drop lvl 1 weapons in market and make fun of people for picking them up.
Spam trade people trying to level.
Pk people in lab.
Pk in mines then leave message on board thanking them for the super gem (make sure you get the person's name for this to work).
I can think of many more but it's late here.
We should work on a 1000 ways to **** people off in Co lol.