"I'll take that for yes."
"I never agreed to that!"

Implied consent is sometimes a legal term, sometimes insidious, and sometimes both. When legitimately used, its basis is that in performing some action that you do not have a right to perform, you imply consent to some terms, generally whether or not you truly agree to them or are even aware of their existence.

An excellent example from U.S. law is that virtually every state has an implied consent statute that allows police to test you for BAC or drugs under the flimsiest pretense and revoke your license or convict you if you refuse. In some cases, this may apply even if you were not driving or in a motor vehicle at the time. In some cases, there may not even have to be any pretense at all. By obtaining a driver's license or by driving (as the case may be), which are not protected rights, you imply consent.

Other common examples are those shrinkwrap licenses and terms of service you click through all the time on the Internet. The GPL has its basis on implied consent resting on copyright.

Implied consent in some form is obviously necessary in society. But it is often abused. Fortunately there are some laws placing limitations even expressed consent.

Here's an example from Maine's website (I recall Pennsylvania having a nearly identical one when I got my license), accompanied by a graphic of the men's room man behind bars:

It is important for Maine drivers to remember that a driver's license is not a right guaranteed under our Constitution.  It is a privilege that is administratively issued and can be withdrawn by the State.  Under Implied Consent, you automatically agree to a chemical test (blood, breath, or urine) at any time authorities have probable cause to administer it.  If you refuse to take such a test for alcohol or drugs, your driver's license will be immediately suspended.  The suspension could be for a period of up to six years.  Because it is an administrative suspension, no court action is necessary.  In addition, testimony from the arresting officer regarding your driving performance can result in an OUI conviction even without the BAC test!

If you are found guilty of OUI based on the police officer's testimony, your refusal to take a test will be considered as an aggravating factor by the judge and another suspension, as well as mandatory jail time, will be tacked on.  So by refusing, you will have a much harsher penalty than if you'd taken the test. 

Remember a test can protect you.  If you are not legally intoxicated, the test will show it. 

All I have to say is that maybe those implied consent types should try living for a year without a driver's license. Now, I agree you don't have the right to drive drunk, but neither does the Man get a license to your Bill of Rights when you get your driver's license.