Some of my faves: Finagle’s Law of Dynamic Negatives (also known as Finagle’s corollary to Murphy’s Law) is usually rendered:
Anything that can go wrong, will—at the worst possible moment
One variant (known as O’Toole’s Corollary of Finagle’s Law) favored among hackers is a takeoff on the second law of thermodynamics (also known as entropy):
The perversity of the Universe tends towards a maximum.
Hanlon’s Razor (or Hanlon’s Law) is a corollary of Finagle’s law. Hanlon’s Razor says “Never attribute to malice that which can be adequately explained by stupidity.”