I think that what they mean by costume party is that they're trying to hide or "cover" things up, like how at a costume party, people are, well, in costume to hide what they're really like in a way. And the line "And I believe this costume party is over before it gets started" means that they're trying to embrace reality and not pretend about anything.
I think that what they mean by costume party is that they're trying to hide or "cover" things up, like how at a costume party, people are, well, in costume to hide what they're really like in a way. And the line "And I believe this costume party is over before it gets started" means that they're trying to embrace reality and not pretend about anything.