When a movie, show, or other form of media suddenly shows breasts and/or sexual intercourse, despite it not having anything to do with the story.
Some very unnecessary boobies:
1. I was watching "Watchmen" last night and had to sit through Dr. Manhattan boning a chick, for no apparent reason.
2. I was watching "Babel" last night and the next thing I knew I was watching a fully nude Japanese teenage girl trying to persuade a guy to have sex with her.
3. The "Requiem For A Dream" lesbian anal sex scene was not exactly necessary boobies..