This term is used in Starcraft 2. It describes the action that a player takes when he forfeits all other unit building and starts building a fleet of Battlecruisers. A player can switch to "full taco" midgame or can have a "full taco" strategy from the start. This is a common strategy among new players, as it requires a shitload of resources to be successful. The game can end before even one Battlecruiser is built.
"I think he's going to go full taco, we should hit early."
"Shit, this aint working, I'm going full taco."
"What's your strategy? I'm going full taco."