What Makes Up the Name: porn + tornado

Then your roommate walks in and you’re all, “Oh, hey,” falling out of your chair, ass rubbing everywhere as you trip over your pants that have now become the ankle chains they give maximum security inmates as your roommate tries to avert his eyes and asks if you're sitting bare-ass in his “favorite leather rolly chair” and you, overcome with the vision of poo streaks and shame, cover your member with one hand and reach up with the other to close the cascading windows of porn pop-ups that have turned your monitor into one big, moaning fleshy pixel orgy, and all you can do is smile and ask him how work was. That’s getting caught in a pornado, class four: uncontrollable porn spam windows take over your screen at a highly inopportune time. You should see a class five.

Origin: It was first posted on the Urban Dictionary in 2004, so who knows. It probably appeared about the same time browsers started getting jacked up by porn sites in the 90s.