This applies to LJ too
1) Continual nudity posts - I get it's your thang (or for your 'Thing'), but it's not my scene and I don't want my screen cluttered with boobs and bits, thank you.
2) People who friend me, then I never hear from them again - then try to add me again. WTF? You wanna talk - pick up the phone.
3) Religion slamming - whether it is promoting your own or dissing another. Peace, love and light, guys.
4) Naming and shaming specific people who have pissed you off. I got rid of a fellow LJer who put someone's name, address and phone number on here, in order to incite anonymous calls to their adversary. Don't do that - it's freaky.
5) Spammers - nuff said.