Now, I can give you all the advise and tips you want about public speaking, but let’s be honest, I don’t know what I’m talking about.
That statement, using the deadpan expression, is funny because obviously this an exaggerated form of a lie. I do know a thing or two about public speaking. This form of humor, self-effacing, involves making fun of yourself.
People love it when someone will make fun of themselves, as it demonstrates that they are confident enough to not take themselves too seriously. Also, by doing so you are demonstrating to the public speaking audience that you are in fact a confident person, which people are automatically drawn to. Most people want to try and build themselves up. Someone who does the opposite is rare and usually draws a laugh.