& Law of Mechanical Repair After your hands become coated with grease, your nose will begin to itch and you'll have to pee.

& Law of Gravity
Any tool, when dropped, will roll to the least accessible corner.

& Law of Probability
The probability of being watched is directly proportional to the stupidity of your act.

& Law of Random Numbers
If you dial a wrong number, you never get a busy signal and someone always answers.

& Law of the Alibi
If you tell the boss you were late for work because you had a flat tyre, the very next morning you will have a flat tyre.

& Variation Law
If you change lines/queues (or traffic lanes), the one you were in will always move faster than the one you are in now (works every time).

& Law of the  Bath 
When the body is fully immersed in water, the telephone rings.

& Law of Close Encounters
The probability of meeting someone you know increases dramatically when you are with someone you don't want to be seen with.

& Law of the Result
When you try to prove to someone that a machine won't work, it will.

& Law of Biomechanics
The severity of the itch is inversely proportional to the reach.

& Law of the Theater
At any event, the people whose seats are furthest from the aisle arrive last.

& The Moccona Law
As soon as you sit down to a cup of hot coffee, your boss will ask you to do something which will last until the coffee is cold.

& Murphy's Law of Lockers
If there are only two people in a locker room, they will have adjacent lockers.

& Law of Physical Surfaces
The chances of an open-faced honey sandwich landing face down on a floor covering are directly correlated to the newness and cost of the carpet/rug.

& Law of Logical Argument
Anything is possible if you don't know what you are talking about.

& Brown's Law of Physical Appearance
If the shoe fits, it's ugly.

&  Wilson 's Law of Commercial Marketing Strategy
As soon as you find a product that you really like, they will stop making it.

& Doctors' Law
If you don't feel well, make an appointment to go to the doctor, by the time you get there you'll feel better. Don't make an appointment and you'll stay sick.
and finally...
& Cole's Law
Finely shredded cabbage.

Pretty good list. I'd like to add some, some that are job specific, but what the heck.

1st law of running phone/data lines:

If the wire is damaged by someone other contractor:
a) they will never tell you
b) they will always damage the first two pairs.

2nd law of running phone/data lines:

If it looks right, it's probably wrong.
If it looks wrong, it'll probably fail its inspection.
If you can't see it, then it's perfect.

3rd law of datacom:

No matter how many tools or supplies you have on the truck, at least once a day you'll have to go to a hardware store to buy a 30 cent part.

Laws of plumbing (Murphy's law)

The smallest hole will empty the mightiest container, unless it was meant as drainage, in which case it'll clog.

Laws of telemarketing:

The number of telemarketing call you receive are inversely proportional to how close it is to meal time.

Laws of tools:

You will not find a missing tool until you replace it with another.

Ant