Mull of Kintyre 'Porn' Test

The Mull of Kintyre test was an unofficial guideline said to have been used by the British Board of Film Classification in the United Kingdom to decide whether an image of a man's penis could be shown.

The BBFC would not permit the general release of a film or video if it depicted a phallus erect to the point that the angle it made from the vertical (the "angle of the dangle" as it was often known) was larger than that of the Mull of Kintyre, Argyll and Bute, on maps of Scotland.

As usual, Wikipedia has the whole sordid story.