Total credit to Finnick Odair for writing these rules. I'm just here to copy/paste and reformat.
Only celebrate happy events here.
No sarcastic threads or threads for bad things, such as bannings or infractions, or other negative events.
Follow The 4/25 rule here.
'Happy Birthday', etc, is only 2 words, so make your post long enough that this rule need not apply.
List of appropriate things to celebrate:
Birthdays, Promotions (Mod->Super Mod->Admin->Site Admin), Modding/PC-related anniversaries, and other special occasions such as ethnic & major holidays, weddings, graduations, births, etc. Basically, events you'd celebrate in real life, as well as on the forums.
Watch for duplicates
Look through the list of active threads beforehand to make sure you don't end up repeating a thread about an earlier event. If there's already a thread for your potential celebration, then just post in the existing one.
Don't post 'Copy & Paste' Birthday wishes
Similar to the rule in The Welcome Lounge, don't simply copy and paste the same word for word birthday wishes on several threads to bump your post count +1.
Ask before making birthday threads!
It's great that you want to help people celebrate their birthdays, but please make sure that the person's ok with you making their thread first. They could want someone else to make it specifically.