You can concoct fake ads, or use real ads that are funny in your presentation.
They can be read aloud, projected, or distributed as handouts. I got an idea for a funny ad from an attorney friend of mine who was hired by a legal temporary service. I used the following flier as a fun way to keep my practical joke company's name in front of clients who were involved in the legal profession.
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 favorites are the funeral monument company that advertised a lifetime replacement guarantee and the sporting goods store that advertised a Back-to-School special consisting of high-powered rifles.