Reductio ad absurdum is a Latin phrase meaning "to reduce to absurdity". It's a debate technique where you take your opponent's line of reasoning and point out that it leads to conclusions that are absurd - and therefore the line of reasoning must have some unseen flaw.
I recently witnessed an argument about whether or not it was safe to use a cell phone while pumping gas. In theory, electricity can ignite gasoline vapors. The consequences are highly undesirable, so you should avoid any risk, right? But think about it - every time you get out of your car in the wintertime, you get a SNAP of static electricity. It's caused by the dry wind against the car's shell, and the arc can be well over 1000 volts. If that open discharge doesn't ignite the lingering vapors at a gas station, what will? And what's the voltage inside a sealed cell phone anyway, three volts? Nine?
Whenever I consider odds like this, I say you're as likely to be hit by a meteorite. If risk is what you're talking about, then the stress of worrying is far riskier than what you're worrying about. Reductio ad meteorite. (By the way, this concept isn't limited to risk, but all the most common examples - say, fear of flying - are about risk. Why? Because people are lousy at evaluating and comparing small risks.)