In fact, most Skittles ads from the last decade or so have often gone right into this territory, including but not exclusive to: a guy who looks like a full-sized humanoid Pinata, another guy who ages rapidly over the course of a few seconds, and an office worker who turns anything he touches to skittles.
Recent Fruit-by-the-Foot ads have involved switching things with it, such as skis. In at least once this included someone's DNA, you can guess how that went.
The Capri Sun "Respect the pouch! Respect it!" ads. These basically consist of a kid either stepping on a Capri Sun pouch, trading a Capri Sun for something, or even simply throwing away a Capri Sun pouch...and being transformed into something.
Fortunately, the tie-in flash games and cartoons show the kids getting along pretty well. They even see their transformations as "freaky powers".
This UK advert for X-Cite breathmints that help you "avoid dog breath". For those wondering, a man sleeping on a couch realizes his breath smells and proceeds to gag and vomit up a snarling, filthy dog. No wonder it was banned!
Fruit Gushers ads from the 90s typically involved folks eating the snack and their heads turned into a random fruits or other objects. Their use of this trope was inevitable. Take 0:18 of this tropical flavors commercial for instance.
This horrifying picture advising tourists visiting Surinam to use protection. The picture is a women with multiple holes in her back. 6 of those holes have an infant inside of it. (scroll to bottom)