Uncle Kenny
I dunno, ninja day seems like it would contradict itself. Not being able to see avatars or the content of posts would make it hard to do anything
wink
You're only thinking of one aspect of ninja, though. Yeah, they're stealthy and everything. But that's not all they are.
Ninja got their start in mountain regions when political enemies fleeing from China sought asylum there. They brought with them a lot of the fighting and subterfuge techniques that we today associate with the ninja. Unlike the Samurai (a warrior-nobility cast), the ninja were farmers, priest and other such humble casts. We could have an item that harkens back to this history.
Also, the characters that make up the word 'nin-jah' mean to "suffer" and "endure". Maybe something based off that.
There are plenty of things we can do for a ninja day. All you need to do is a bit of research and no rely solely on their pop-culture conceptions.