See the title. most off the time when a spongebob uses its rage. the server crashes or atleast has a change to

chance*

Server crashes are due to the orangebox engine's handling of overflowing stringtables, they leak into each other occasionally and inconsistently on servers with high levels of custom content.
No particular boss or rage causes crashes.
It's something that has to be lived with until either stringtables are increased in size or overflow handling is improved.