The term 'Spack' is used to describe someone who above all else, proven to be exceedingly dimwitted, this person isn't a few sandwiches short of a picnic, oh no no no, they forgot the whole fucking picnic basket.
This is an insult best used on friends or people who you know know the
definition of it, because when used on an actual Spack, they will not know the sheer
gravity of the insult that has been
dropped upon them due to their lack of intelligence, and therefore the impact of the insult is lowered significantly.