Sides of buses
The Good Doctors have drawn a correlation between the fact that a movie that is advertised on the sides of buses (both double and single decker) is likely to be of a lower quality than those not advertised in such a way.
Once listeners began to cotton onto the theory, they began contributing their own conclusive evidence. Mark rebuffed some but conceded that "Spiderman 2, which I liked, had massive bus advertising - but then again, so did Sex Lives Of The Potato Men." Colin Murray suggested that the rule be changed to "no good comedies are advertised on the side of buses," but frankly, who cares what he thinks.
Also the source of some amusement when the posters are installed incorrectly - the prime example being a Fifty Shades of Grey poster that ended up reading Fiftys Of Grey Hades. This was deemed to be a more accurate description of the film anyway.
Not to be confused with the rule about films advertised on Phone boxes. Except that that one doesn't work either, owing to the Shaun Of The Dead exemption.