[johndallman]

Clueless [-10] is a mundane mental disadvantage, whose effects are mostly social. You don’t get the fine details and nuances of human interaction, which gives you -2 to reactions from most people when they realise it. This disadvantage appeared during the GURPS 3e period, probably in GURPS IOU, whose large stock of mad geniuses, hopeless nerds and weird aliens really needed it for characterisation.

Specifically, you usually fail to grasp colloquial language and humour aimed at you (IQ-4 to realise you’re the subject of a joke), cannot engage in sophisticated conversation (-4 to Savoire-Faire) and usually don’t realise when someone is trying to influence you via Sex-Appeal (+4 to resist).

This is not No Sense of Humour: you can enjoy written and physical humour, and make (bad) jokes yourself, but you’ll miss other’s witticisms. Nor is it Gullibility, since you have no special inability to realise when people are trying to take advantage of you, except in social situations. Those can be bad, since you’re at -4 to resist Fast-Talk on subjects like the interest of members of the opposite sex in you. There is a small upside, as anyone trying to use Rapier Wit on you is at -2 to their roll.

Most clueless people also have weird or annoying habits related to lack of social awareness, and you can take one or two of them as additional quirks. As far as I can see, this disadvantage is pretty much incompatible with Empathy, Smooth Operator, and other social-interaction advantages. It won’t keep you from having Wealth, Status and the like, although achieving them by your own efforts may have been hard. The Discworld RPG has a Literal-Minded disadvantage that is worth less if you’re also Clueless.

Clueless is a reasonably common disadvantage option on templates for technical or preoccupied folk, species that are naturally solitary, or come from societies very different from a setting’s reference society, and the less sophisticated AIs. Like most Mental disadvantages, Madness Dossier has drugs to cause Cluelessness, which would actually be effective in damaging the credibility of witnesses. Power-Ups 6 has a quirk-level version, and Zombies are often Clueless, if they have enough mind to qualify for it.

I don’t think I’m entirely clueless, but I have some aspects of it. I’ve never put it on a PC of mine, simply because roleplaying it would make communication harder in a game session.