The act of slapping an unsuspecting individual as hard as possible across their forehead and shouting 'Spam'.
This can be countered by holding a guarding hand across the forehead, if suspicious of an approaching attack. This led to the development of the 'Neckback' which followed a similar path as the 'Spam' but involved slapping the back of the neck. This is also known as MAPS - spam backwards, you see.
When a double guard was developed, involving a person holding both their forehead and the back of their neck, a third route of attack, the 'Lipblap', was unveiled. This involved slapping down at a persons mouth (when they were talking for best effect) causing them to sound stupid and make a wet blubber noise. The beauty of this third attack meant that even when guarding, there was always one route of attack open - although the attacker now had to be quick to find the ungauarded area, and (especially with the 'Lipblap') the confusion tended to result in a simple face punch.