Murphy was a cop
Bulletproof vests aren't.
The bigger they are, the harder they fall. They also punch, kick, and choke harder, too.
The speed at which you respond to a fight call is always the slowest legal speed. You want to arrive in time to arrest the winner and put the loser in an ambulance.
OC works on cops too, and regardless of wind direction, will always blow back in your face.
High speed chases will always proceed from an area of light traffic to an area of extremely heavy traffic.
If you know someone who tortures animals and wets the bed, he is either a serial killer or he works for Internal Affairs.
Placing your pistol back in a holster with your finger on the trigger will cause you to walk with a limp.
Flash hiders don't, nor do silencers.
If you have cleared all the rooms and met no resistance -- Congratulations: you kicked in the door of the wrong house.
And so on.
Note: repeat after me; I will make sure the link is good when blogging when I'm tired...