Two Shits is a measurement, standardized under the SI system of measurements, used as a yardstick to determine how much one cares.
The idea of using how many shits one "gives" to measure how much that person cares originated with Sir Isaac Newton. He first put forth the idea in his Philosophiae Naturalis Principia Mathematica, published in 1687. In it, Newton suggests that "hee that doth give a shite, knight'd shall hee be."
After Newton, the idea was expanded by James Ivory, the eighteenth- and nineteenth-century Scottish mathematician. Ivory established the Limit Theorem of Shits, which stated that there is a specific range of shits it is possible to give in order to care. Tragically, Ivory died before he could calculate what has become called "Ivory's Constant," Two Shits, in his honor.
Ivory's Constant was finally discovered by American scientist Robert Oppenheimer before he began work on the Manhattan Project. It was heralded by President Franklin Roosevelt as "a shining light for mankind," who held that "the fifth freedom is the right to give two shits."
Scientists at the Institute for More Shits in Bern, Switzerland are hard at work applying Ivory's Constant to real world situations. It is believed that if people who give two or more shits could be discovered early, they could be the shining diplomats of the political world.
Another leading hypothesis being tested is that Ivory's Constant could be used to make things more powerful. For instance, currently lightning is a minor force of nature, the "kid brother" of more powerful "acts of God," such as floods or hurricanes. However, if lightning were made to not give two shits about the laws of nature a new kind of lightning, "super lightning," could be made. Super lightning would be a useful weapon for the militaries of the world.
Currently Congress is looking to pass a law that will be the standard in Two Shits measurement in the United States. Unfortunately partisanship has stalled the passing of the bill due to disagreements as when it can be invoked. As of now you only see it once a year on Sept. 11th during an election year to make the prospective candidate look like they are sympathetic to the registered voters of their party. Focus groups also cannot agree on whether Two Shits should be exclusive to the U.S. or opened up to a broader worldwide audience. That's why it is on the docket for discussion at the next U.N. session for the Two Shits World Alliance Conference. The dung is piled high and eventually a standard will be formed but don't hold your breath.
edit The Upper Limit
All efforts to discover the upper limit of shit-giving predicted by the Limit Theorem of Shits have failed. This upper limit, called the Big Blubbering Baby Constraint, is believed to be what separates everyday people from U2 lead singer Bono.
Once an individual reaches the six shit level of caring, they officially give a fuck. This has been proven through multiple double-blinded random control trials (p<.05).