Where i can report this

[Arasy]

[Calamity]

I don't think this would get him/her banned for sure though childish, "weak guild" insults are pretty harsh.

According to the rules here: http://forum.celestialuna.com/index.php?/announcement/10-server-and-forum-rules/

Grief Play and Harassment
Grief Play/Harassment is playing in a way to upset or ruin someone elses play.
This includes:

• [GM Decision] Swearing at someone
• [GM Decision] Insulting someone
• [Warning Needed] Spamming someone with unwanted private messages or notes
• [Warning Needed] Stalking/Following someone around when they don't want it
• [Warning Needed] Kill Stealing (KS). Attacking another players target without permission)
• [No Warning Needed] Spot Claiming
• [No Warning Needed] Assaulting someone's character (such as "Don't buy from zxy123 because he's a liar and cheat")
• [No Warning Needed] Mob Dropping (gathering an aggressive mob near another player then logging off, teleporting or dying)
• [No Warning Needed] Anything else a GM justifies as Grief Play or Harassment

Punishment is typically a Ban between 5-15 days. Repeated or extreme cases will result in a Permanent Ban.
Harassing staff will result in a Ban for however long they feel necessary.
[Warning Needed] - For the rules requiring warnings, you will need to provide at LEAST 2 screenshots.
One of you warning them to stop, and the second showing that they didn't.
[GM Decision] - Provide as much evidence as possible, it'll be up to the GM who takes your case what to do about it.

 

If you insist on reporting him/her, you can post it here http://forum.celestialuna.com/index.php?/forum/14-character-report/

(you need to have a post count of at least 10 to be able to make character reports)