One line of commercials for Denny's restaurants had people performing stupid stunts, like trying to throw a cow or a human slingshot. At the bottom it reads, in the usual tiny white text, "Do not attempt, professional idiots".
If the commercial doesn't concern a consumer's health or safety, it's not likely to get the attention of the FTC. There's another large area of commercial advertising that's regulated, and very strictly, by a different body.
If a child recreates a stunt he or she sees in a commercial and is injured, the network that ran the ad would take the heat. Other times, the advertising client's legal department will demand a disclaimer to avoid potential lawsuits. This decision is usually made by the client before the commercial is even in the can.