A real life example would be Operation Fortitude, where the allies fooled the Germans into thinking the real liberation forces landing in Normandy were actually a diversion so that he would keep the majority of his armed forces where the Germans expected the real liberation force to land.
Likewise, earlier they'd convinced the Germans that the coming attack on Sicily was a diversion and the real attack would be a two-pronged assault on Sardinia and Greece. Winston Churchill said anyone but a fool would know the target must be Sicily, but British intelligence made the Germans believe that was what they wanted them to think.
Variants of this line were used when The Texas Seven escaped from the John Connally Unit in Karnes County, Texas. Whenever someone walked into a room they were trying to escape from, they used some form of, "Hey, what's that behind you?" and managed to trick sixteen people this way.
Another example of this as a prank is to hold up your hand, say "Hey look at this," then when that person looks, slap them with the other hand.
Almost as cruel is to point and ask: "What's that thing on your shirt?" - and then, once they're looking down, bring up the pointing finger to hit them in the nose.
A much simpler version is to say: "Look at my thumb" - and then, once the victim is staring at your thumb, remark: "Gee, you're dumb." In Animal House, this gag is coupled with a "Hey, You!" Haymaker.
Wild Bill Hickok once saved his own life by doing this. A drunken man with a rifle had the drop on him, when Hickok looked past him and yelled, "Don't shoot! He's just drunk!" The man spun to face Hickok's imaginary friends and was shot through the temple.
A glorious example was recorded in the 17th century 'Schoole of the Noble':
"The Master and usher of a school had upon occasion appointed the field, and their weapon was each of them a two-handed sword, and meeting at the place appointed said the Master, 'Thou art not so good as thy word.' The usher asked him why. 'Marry,' said he, 'thou promisest to bring nobody with thee and yet looke yonder what a number of people are coming towards thee.' The usher no sooner looked about, but the Master smote off his head, and afterwards meeting with some of his friends said, 'I have taught my man a new tricke in the field,' said he, 'which he never learned before.'
