Jokes need a twist at the end, your essentially leading someone down a path then move quickly in another. This is crap but eg "Hi everyone, my name is Luke Walker. Now I know what you're thinking, and no, my middle name is not sky. That would be ridiculous. I'm not a Jedi, I don't own a lightsaber and I've never forced choked someone (well not outside the bedroom anyway). No no. If you must know, my middle name is actually cunt." - Take them one way, then switch :)
Also, be careful of your use of words, you only want to add what's necessary. For instance, the alcoholic part is not necessary. I struggle with writing too, but you get better. Write exactly how you would talk. Finally try improvising out loud on your own while recording it, then later writing down the best bits. I get a lot of good stuff from that. Good luck bud!