How to make yourself hated:
Don't actually do these. Some are funny, some are downright nasty.
1) Join a group for a quest that says 'In Progress' and where the quest starts in an explorer area (example: Prison of the Planes). Make your way to the quest entry. Once you are just outside the quest, ask people for directions. While they rage at you or give directions, grab a coffee. Return and enter the quest.
2) Join a Shroud group as the 12th person. Ask for an invite to a +2/30 resist guild ship. Bonus points if you are in a guild with those amenities on your own ship.
3) Join a 'BYOH' group. Get into the quest and summon a divine hireling.
4) When you are holding a level, apply to join a Bravery group, then after you are accepted take your level (pushing yourself out of the level range) and do the quest. (You can get the same effect at some levels by summoning an Onyx Panther but that is more obvious, if you do the level up trick right people will blame the group leader more than they blame you)
5) Join a PUG group for an in progress quest, particularly one where groups usually want to be full. Step into a totally unrelated quest and go and make yourself a coffee. Epic VON6 is great for this - they can't kick you without losing VON5 progress.
6) Post a level 20-20 LFM (25-25 post MOTU) for a quest players run at max level (so your LFM appears at the very bottom of the list). In the comments field type lyrics from 'Call Me Maybe' (or another awful, catchy song) so that everyone that looks at the LFM panel gets that song stuck in their head.
7) Hold your push-to-talk button down for the entire quest or raid. Works better when someone in real life is arguing with you or when you are playing awful music.
8) Post extremely overpriced items in the Auction House (say a +1 Holy Shortsword for 1.2m PP), and then ask people in General Chat 'Is a +1 Holy Shortsword really worth 1200000 platinum?'
9) Join a group for a raid that is marked 'Elite' and then start talking about how this raid is super-hard on Elite and we'll wipe for sure. Bonus points if the raid is the Reaver's Fate.
10) Join a group for a raid that has a lock-in barrier (like the lock at the start of ToD). Just after passing that barrier, say you need to AFK. Don't come back until the quest is finished.