Step 1: Write a .dll that interposes on common windows controls used to display EULA messages.

Step 2: Whenever this .dll sees common EULA agreements, it randomly modifies them before displaying them. Changes "SHALL" to "SHALL NOT", changes "GPL" to "Public Domain", changes "may not be duplicated" to "ok to post to piratebay", etc.

Step 3: Embed this DLL in a self-replicating, self-destroying virus/worm. It spreads, stays on a computer for a random amount of time, then erases all evidence it was ever there.

Step 4: "Your honor, there's no way of knowing what I agreed to, since there is no permanent record and the current license does not match what I remember. Perhaps I had the EULA-modifying virus at the time."