I have wondered about this one too as Kai is the name of several of my pirate friends. I have not been able to think of any way that name could be used inappropriately. I kept forgetting to post it so great call on getting this one in.
This is an interesting one since we thought we had added Kai to our list of acceptable words back in May 2013, but it looks like it didn't stick. We'll be looking to add it back in one of our upcoming updates.