I'm in a radio session today, working on a funny* spot. The script was funny when I wrote it, but by the time I get to the studio, I've rewritten it dozens of times. I've read it dozens of times and presented it maybe a half dozen. Then the talent reads it a few dozen more. And after awhile, I often find myself in that place where I'm going "Wait, is this really funny?"
Unless you're in a joke-writing class, analyzing humor can be counterproductive. If you have to explain why something's funny, it's not. Funny just is. Humor is based on surprise, so after the surprise has worn off, it's hard to keep that sense of what's funny. Because of that, the best gauge of whether or not something is funny is usually your first gut reaction.** Trust your gut. And when you present it and people laugh, point that out to them if they come back later and say it's not funny. When you hear 50 takes and one of them makes you snort in laughter, note that.
Humor can be structured and built up, and a script might go through months of painstaking crafting and revision. But you'll know if it's funny in about a half second.
*Yes, funny is subjective. For the sake of this post, though, pretend I'm talking about an idea that is indeed "funny."
**This is different from late-night slap-happiness funny--if it's not still funny in the morning, it's probably truly not funny).