If you're Terran, build an Engineering Bay behind someone's minerals (in Fastest), or close enough to fly it over easily. Try to do this before they get much resources; it doesn't work well against other Terran players since Marines can attack air. Anyways, you fly it over their mineral node so that it's impossible to click the resources. Have your SCV or something attack their Nexus / Hatchery; hopefully they'll make most of their peons attack your SCV or unit (if you do it before they get infantry). Afterwards, they'll realize that they can't right click their minerals and are stuck with whatever workers they have mining, if any. I did this to a guy, and he made a Photon Cannon and he couldn't do anything until he could free up the air over his minerals; it made him waste about 5 or 6 minutes,
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Or do the worker stacking glitch to own the enemies command building (in fastest again). if you can kill it early on, then they're screwed. Both of these are also usefully deployable as backstabbing techniques.