Ruin the Active of the person above.

So it is really simple actually. Someone creates an active effect for an item (like Zhonya's Active), and the next person makes it absolute garbage by putting it on an item that makes it worthless or has no synergy at all. (if you put it on something that already has an active, it would replace the active on the item)

So an Example would be like:

Unique Active: Dashes to the target of your last auto attack (within the past 5 seconds). 120 Second CD

Ruined by: Put it on Runaan's Hurricane, so it goes to a random one of the 3 targets that was hit (whichever got hit last I guess) And it usually is bought by champions that don't want to be in the middle of the fight. Now it could open an interesting escape for champs with long enough AA range (Auto a jungle mob and blink to it), or be used to catch someone who is escaping at the end of a teamfight, but it still is kinda ridiculous to be put on that item in particular.

So, the person who starts gets to try to ruin this active P:

Unique Active: Deals 80% of your armor to an enemy champion as physical damage, and 90% of your MR as Magic damage. 90 Second CD.