How am I supposed to write a joke? I think it’s something like…

setup
The Setup — Establishes the premise of the joke by providing the audience with the necessary background info. The setup should be as tight as possible (new open mic comics tend to ramble on with unnecessary details).
The Punchline — Wham! The laugh line. The setup led the audience in one direction, and you surprised them by suddenly going off in a different direction. That twist, that element of surprise, is a punchline’s chief ingredient.
Tags (optional) — Also known as toppers, tags are additional punchlines. Sometimes they build on the original, sometimes they twist and snap back and forth in surprising new directions. Think of a skiier slaloming back and forth, twist, twist, twist…
(found here in the interwebinet)

For example…
I love getting older. I know so much shit now that kids don’t know. Well at least I’ve decided to forget about shit I never figured out.
Like what’s the difference between a bison and a buffalo? You know that, right?
All the kids are going, ‘yeah, what is the difference, their the same thing right?’
All the geezers are going, ‘I don’t know. Who gives a shit?’
Or, like, a girl cow is a cow and the boy is a bull, right? Well, what is the generic word? A bovine? That doesn’t make any sense. Kids are going, ‘yeah” and they’re trying to look it up on their phones. Geezers are like, ‘Bovine. Cow, cattle, I don’t know. Who gives a shot?’
Really, it’s the best part of getting old. The ‘who gives a shit’ factor.

In case you hated that one, here’s on you’ll really hate…

I don’t know if it’s about getting old or just being a dude. But my favorite thing is just doing nothing. My wife asked what I want to do for my birthday and I said, ‘nothing.’ Of course she was like, ‘come on. What do you want to do.?’ I was like, ‘really. Not a goddamn thing. I just want to sit on my ass and fart.’
‘Really? Don’t you want to go out and…’
‘Look. If I die in a gas explosion while I’m doing nothing but picking my nose, you can tell people at my funeral that at least I died doing what I love!’

Not sure how funny those are but it’s all in the delivery, right? And I could make anything sound funny. Wanna bet me?