To take a subset of the topic at hand, I think Mencius nailed it when he defined corruption. To very roughly paraphrase, corruption is a mismatch between formal and informal power.
Acton's famous aphorism can be rewritten in the following form: 'Those with formal power tend to use it to increase their informal power'.
"Without ego corruption does not exist"
Not true at all. This simply rules out corruption due to greed. There are tons of people who do corrupt things for 'noble causes'. Just as a quick example, regardless of the truth of the component claims of Global Warming, there are tons of people who commit corrupt acts with an eye towards relieving global warming.
The examples you give are worded similarly, but are actually quite different. I'm pretty sure you actually meant:
A builder, or a secratary, who looks out for his friends and does them favours is... a good friend.
A politician who does the same with public resources is... a corrupt politician.
A sad bastard who will sleep with anyone he can is a sad bastard.
A politician who will sleep with anyone he can is using the power of his office to coerce those under him.
You will note that in all cases, the politician has expanded his imformal powers to be greater than his formal ones.