This ad appeared in the British Yellow Pages The title is of course already double in itself. But if you turn the picture upside down and cover part of it, you can see a young girl fingering herself. I think this is the most convincing example of a subliminal ad, possibly also a joke. What else would the picture of a drinking woman be doing on an ad for flooring ?
In the Disney movie The Rescuers, one of the animators built in a joke. During a flight scene, something odd is visible in a window in the background. This would be barely visible in the movie, but it's very clear in this frame : a naked woman in the window !
Coca Cola advertised in Australia with this poster, somewhere during the eighties. Until someone discovered what could be seen in the ice cube on the right ... That's not a bottle she's going to put in her mouth ! The artist, which probably thought it was a good joke (it was), was fired and sued. All posters were recalled and a new campaign was launched.
This is a hilarious example of what happens when you design a logo without checking it afterwards or asking a second opinion. About half of all people will first see a naked woman's torso here. I did't even know there was also a dancing couple until I read the title of the ad.