A character may be defined as incompetent in any one skill, for -1 point. He cannot learn that skill, and any attempt to use it is at an extra -20. Incompetence is considered a mental disadvantage, even if the skill is physical. The character is simply inept, or has a mental block against learning this type of skill. You cannot be incompetent in a single specialization; if you are incompetent with Guns, for instance, you are incompetent with every type of gun. No character should ever be allowed more than -5 points in Incompetences.
The GM may disallow any incompetence that seems silly or abusive in his particular campaign. Likewise, the GM can allow an incompetence or two to count as quirks, if a character is already at the maximum point value allowed for disadvantages.
So, what do you all think? Along with quirks as optional rules, these could make for some highly detailed and well defined characters. As a GM, I would ask that each incompetence and quirk be given mention in the background story for the character.