TBH the "The Final Solution" bit isn't that bad unless there was actual context to it suggesting it (in which case, get rid of them ASAP)
(EDIT: "actual context" means: anything remotely suggesting death. Otherwise, could be for destroying asteroids.)
OTOH, they probably should've expelled him just for calling someone a slave
This is his third offense this year though. 1st one was calling the black kid a slave. Second was kicking someone in the nuts (although this was due to that kick-ee insulting him) and the third of course was the rockets name "The Final Solution."
The 3 add up to an expulsion imo. I wouldn't expel someone for any of the individual incidents as long as he promised not to do it again, but they realized he would continue doing these things.