You can still be a dweeb with a high charisma score, You just never learned to be persuasive or use your natural charisma.
Warlocks use their charisma a lot, so i wouldnt recommend a low score, they need it for damage, DC and some other special abilities.
Hmm, I can certainly see an asshole high charisma character, but not sure about a dweeb high charisma. When I think of "dweeb", low charisma is pretty much the first thing that comes to mind. Wouldn't that be like trying to play a high strength weakling or a clumsy high dex char?
Anyway, I'm shelving my nerd cultist character as poor warlock material and now thinking of a half-elf high dex high charisma buxom adventuress. Start as a rogue for skills and a bit of sneak damage, then go all warlock - fey patron, blade pact. Was thinking of at least 3 levels of rogue to grab swashbuckler for some survivability through strike and dash attacks. Sneak damage is going to be low, but between hex and blade invocations it might still be worth it.
Way less effective than a simple range blast spamming fiend warlock might be, but that just sounds boring compared to an elusive bitch with a wicked blade.