Context is important.

> to celebrate the person that passed

It is clearly written that such celebrations are for the person who has passed.

It isn't even implicit: It's literally spelled out, in very plain English, what the purpose of these celebration are.

> I hope people get together and celebrate when I die.

Here, it is clearly written that the author hopes that people will perform such a celebration for him when he does eventually die.

Not because he is dead, but because he has lived. That's what celebrating a person means.

Everyone understands this. It was a joke. It is funny to propose that the commenter hopes that people will get together and go "wow, thank god that asshole has finally kicked the bucket" and this proposition is made possible by the fortunate coincidence that "get together and celebrate when I die" can, divorced from context, be interpreted in either the intended way or the funny way.

If we're talking semantics, the celebration is not so much for the deceased, but for the living "left behind."

Prepositions are a fundamental part of English, and having a celebration for a person [alive, or dead -- it doesn't matter] is using "for" as a preposition.

You can obtain the proper context from GP's whole comment. They were talking about celebrating someone's life after they passed so it's natural, contextually, to assume celebration of life.