First let's take a look at the usual definition:
The Second Law of thermodynamics says that everything tends to go from an ordered state, to a disordered state. Thus, there is no way that life (order) could have risen from a pre-biotic soup (disorder) or even increased in complexity (order) as it supposedly evolved.Hm. That definition that creationists use so much seems to be missing something....
Similarly, the Big Bang must be wrong because it says that the universe started off in an explosion (disordered) and spontaneously formed galaxies (ordered).
Oh yeah! That bit about closed systems and energy not being put into the system! We'll let's add that back in and start testing the second law out in a thought experiment.
Let's imagine I have a pot of water. If we take a look at water at a molecular level, it's rather disordered. The arrangement of the molecules in regards to one another has no rhyme or reason.
As I just noted, if you add energy to the system (boil it), using the creationist definition with that bit about adding energy actually added, this would indicate that we should see more "order". However, the exact opposite is the case. If energy is added (ie, heat) the water turns to gas and there is even less order. In the other case, if energy is removed from the system, it becomes ice which, on a molecular level, is a highly "ordered" crystalline structure.
The second law got it backwards! Looks like I've disproven it.
I can has Nobel prize now?
Note: This is not actually intended as a proof against the second law. Rather, it's a demonstration of how pathetic the creationist definition really is. For a more comprehensive definition, take lots of math and science and eventually a few courses on thermodynamics. Or just visit the Talk Origins page on it (which still requires a bit of Calculus understanding).