The act of jinxing something so badly it proceeds to happen instantaneously with no warning. Often happening when least expected and/or in discussion.
*two friends in the middle of a race in a racing game*
Friend A: Good luck winning, my car has the best engine.
Friend B: Not if it brakes down.
Friend A: Nah, its the most reliable engine as well.
*Friend A's engine brakes down litteraly 2 seconds later*
Friend B: Well thats the Viner Effect for you.