The song Lava is about how Fred is despondent and how, meanwhile, Kate and Cindy hate his guts and wish that he was dead. Toward the end Fred says "I'm gonna jump in a crater". In context, he means jumping into the crater of an active volcano. If he didn't die from the impact, he would quickly be burned to death by the molten rock. Rather than try to talk Fred out of this course of action, Kate and Cindy instead respond in unison "See ya later", which clearly conveys their happiness at the thought of Fred killing himself.
The song Lava is about how Fred is despondent and how, meanwhile, Kate and Cindy hate his guts and wish that he was dead. Toward the end Fred says "I'm gonna jump in a crater". In context, he means jumping into the crater of an active volcano. If he didn't die from the impact, he would quickly be burned to death by the molten rock. Rather than try to talk Fred out of this course of action, Kate and Cindy instead respond in unison "See ya later", which clearly conveys their happiness at the thought of Fred killing himself.