Something all human beings have the right, and the moral responsibility, to do, if/when their current system of government or society no longer performs legitimate functions. Said right is guaranteed in the United States Constitution and is immortalized in the prose of Thomas Jefferson.
The British taxed us and tried to take our guns...
Bill Clinton and Janet Reno shot people and torched buildings full of people...
The result? American Revolution. Timothy McVeigh. Rebellion.
From the skater and phreaker slang "okay rad" (rad was short form of 'radical') commonly shortened to "kay rad". Was shortened to "krad" in text communications, possibly spawned "kthx".
Skater 1: "Gonna meet up here tomorrow?"
Skater 2: "Yeah!"
Skater 3: "kay rad."