You can concoct fake ads, or use real ads that are funny in your public speaking engagements. They can be read aloud, projected, or distributed as handouts.* Watch for funny ads that relate to your business or presentation topic in magazines and other periodicals. Cut the ads out and photocopy for distribution as a handout or make them into slides and overheads. Jay Leno has a series of books called Headlines I, II, and III. Besides having really funny headlines from newspapers and magazines, the books have lots of blooper advertisements along with commentary from Jay. My favorite was the funeral monument company that advertised a lifetime replacement guarantee.
You can read these aloud in your public speaking engagements without worry of copyright infringement. Always attribute the source though. You don't want to claim material as your own if you did not create it.
*Be careful not to violate copyrights