the_truth, no offense, but you post reminds me of dubya bush and his "you're with us and against us". An important concept in logic is the difference between merely contradicting and what is known formally as "contrary" opposition (being on the complete opposite end of a spectrum). To prove something false, you do not need to show the "contrary" fact to be true, only a contradicting fact.
Example:
Let's say that someone claims, "I am super-humanly intelligent."
To disprove this person, you do not need to show him/her to be a moron. You only need to show that the person's intelligence is not above the level of genius.
Another example:
Someone claims, "All desks are brown."
To counter (contradict) this claim, you do not need to show that all desks are not brown. Rather, you only need to show that at least one desk is not brown. The statement, "Some desks are brown, and some are blue" contradicts both the claim, "All desks are brown" and its contrary. (For simplicity in this example, assume that all desks are only of one color.)
So, how does this relate to your post?
You stated, "Prove you are selfless, jog a mile in a public area in complete nudity, immediately." This, I assume, would be to show that a person could be absolutely selfless. This is the contrary to "All actions are motivated by self-interest." However, you do not need to show the contrary, only a contadiction. If it is not true that all acts are selfless, it does not mean that all acts are self-motivated, and vice-versa.