Playing Command and Conquer 3 Kane's Wrath, I'm the Scrin (Alien race) and I've got a few Annihilator Tripods (Heavy walker, anti-vehicle anti-structure) out, one of the enemy AI (Set on Normal) is one of the Scrin sub-factions and has their superweapon, the Rift Generator (Works by creating a small temporary black hole over a certain area, ejecting anything in the vicinity into space, has a recharge time of 7 minutes, deals damage over time, but stops units in their tracks), out on the other side of the map, behind another enemy base.
A few seconds left on its countdown, and using the Wormhole support power, I was going to warp my Tripods to the revealed area around the Rift Generator, the Tripods have a close range EMP attack. Got the wormhole set up next to their Rift Generator, and was about to set the second one down and just as I set it down, they activate it right above my Tripods, when it would have been absolutely impossible for them to know my units were there from the Fog of War.
It didn't cost me the game, but it was infuriating because there was no way for them to know my units were there. Fucking cheating AI.