There are rules that are based on mathematical formulas which, if you don't use common sense, will become ridiculous under extreme circumstances.

Two examples. Two different (swedish) RPGs, from memory:

The carrying rule: You move slower the more you carry. However sooner or later you will start moving backwards. At increasing speeds.
(Basically the rules do not specify that you stop at speed 0). Theoretically you could, if you carry enough, go at the speed of light. Backwards.

The Explosions do more damage in small spaces rule: Another game tries to emulate that hand grenades etc do more damage if you are in a confide space with them when they go boom.
However the formula used "breaks thru" at a certain size of space and well... The end result before it was corrected in a later edition made you HEAL if you pulled the pin from a grenade, held it in your hand, and managed to squeeze yourself into a standard size old-fashioned outdoor trashcan (the kind you have standing in your yard). The number basically went haywire when there was too little space between you and the wall.