There is only one type of best man speech...and that's a really funny one. I often speak to guys who say that all they want to do is get up there, say a few lovely words about the bride and groom, toast them and sit down. Well, do so and repent at leisure.
Whether you like it or not, everyone is expecting you to make them laugh. We all know that the best man speech is billed as the entertainment, and if you don't step up to that role, then there are going to be a lot of confused and disappointed people. In most cases people want to go for a short speech because many best men are paralysed by the thought of making a room full of people laugh, and I completely get that. Making people laugh is a hard won skill, and it takes a lot of thought to get it just right. Those guys that can just rock up and do it effortlessly are few and far between. However, you can't run from that challenge, because you're missing the point - this speech isn't about you, it's about the groom.
Yes, you might be worried about being funny, but the groom is expecting a comedy send off and it's your job to deliver. You've got to remember that the guests are all on your side, so they're willing and ready to laugh along with your speech, and if it goes a bit wonky, they'll love you for trying. And nothing beats the feeling of sitting down to raucous applause and laughter. You've got to believe you can do this, and it's far better to have tried than to give up before you start.