Logged evryone out then if they wish to log in tell them that your ;)password has recently been changed. Or when everyone opens their account they can't post while giving a warning that you are banned on this forum for some reason.
This could be savage
Edit: or giving random people red trusts then tagging those as happy april fools s*cker lol
Definitely everyone will freak out when they found this like having cold sweat while almost had a heart attack, thinking what you've done for being banned. I can now imagine our faces when that happen and you realize later that day is when everyone making shit out of you.
Hope Theymos won't consider this haha.