I have in the past replaced everyone's avatar with a random blinkie from a folder of 100+ of them. Feel free to grab the collection I used last year here: http://www.x-h2o.com/vb/blinkies/
On VB, I once started a thread and used the [me] mod that replaces that with their username and made up this long diatribe about how they had been using way too much bandwidth so we'd have to shutdown for a couple of days, etc. That was pretty good, it took a while for people to catch on.
I also used the self-ban deal where I "gave everyone banning rights" but when they tried to ban someone, it banned them instead for 15 minutes. It made for a very quiet day...
Probably won't do anything this year, unless something especially devious comes to me. One year we turned the text upside down, and backwards. Another year (back in vB days) we had all posts miss out the vowels in the words for certain members. Another year we had members who, whenever they tried to post, got a message saying "no.. no soup for you" when they hit post.......
We write and publish editorial type announcements on our home page.
In the past:
- Justin Bieber to go off-road racing (the genre of my site) . We did the drawing of his proposed livery etc.
- A new revolutionary off-road race that gets hosted by two rivaling race promoters. We created a joined logo for them. Both promoters got overrun by phone calls. I still hear about that prank from a few years ago.
- depend (the adult diaper company) to introduce a racing diaper.
- Some media giant to buy us out.
My prank for this year is that whenever a member creates a post, the post will no longer be under their name and instead will be posted with a different registered username/member. It's awesome it's confusing a heck of a bunch of ppl haha. I also did that for TaigaChat and replaced April Fools with a different phrase.