The hottest new advertising trend around is to get consumers to do the advertising for you--and the "make your own viral video" is, or rather was, quickly becoming a favorite technique. Until poor GM discovered that if you let people make their own videos, and you upload them to your site, and you don't actually look at those videos before you put them on your site, and your big American SUVs happen to be an easier target for environmentalists than the Exxon Valdez...well, you get this. Which is great for the rest of us. But not so good for the Chevy Tahoe. Sorry, GM. There's a reason that viral is a term originally reserved for communicable diseases.