1. When a pornographic movie unexpectantly becomes a beastiality movie by the introduction of an animal at the point when the viewer is usually fully aroused, often to the disgust and dismay of the viewer.
2. When a male animal is introduced into a pornographic movie, often taking the female actress engaged by complete surprise.
3. When one is viewing a pornographic website and is unexpectedly exposed to questionable or relatively disgusting or unarousing material.
4. Any unexpected boner killing material found in a pornographic movie or website.
The term is used as an expression of surprise and disgust.
That ambush horse cock totally killed my boner!