I've been working on the pass pages for FML over the last couple of weeks. This is pretty much my last chance to make any changes before the book goes to print.
One of the things I've been paying close attention to are the jokes. The thing about being funny in books is that it's hard. Some humor is universal but most relies on the reader to have some kind of knowledge. Some jokes only seem funny.
So when I do revisions and copy edits and pass pages, I'm reading these jokes many, many, many times. And the test for me is whether the joke remains funny with each read or if I begin to cringe when I read it. If it remains funny, I know I've got a winner. But if I start to have doubts about it after the second or tenth or twentieth read, I remove it.
To me, that's why the revision process is so vital...especially if you're writing funny books. But the same methodology can be applied to emotional scenes as well. In my book The Walls that I spent about 2 years working on, the end scene still makes me tear up to this day, despite having read it more times than I care to admit.
When you're writing something funny, it should be able to stand up to repeated readings. If it doesn't, it's time to consider taking it out.