Primarily Vulcans, for a variety of reasons both good and bad. I (like to think I'm) fairly logical and dispassionate when reasoning (good), but I'm also (mildly) deficient socially - I don't often initiate social interactions and occasionally miss social cues, though less than I used to.
I don't know that I'd call Vulcans socially deficient. They simply manifest social graces differently than most. Only human arrogance would suggest that a behavior different from their own is somehow less socially acceptable.
Vulcan has its own kind of social etiquette. I wouldn't call Vulcans deficient in that area - they can clearly even interact with Humans quite well. They wouldn't call Humans socially deficient, so the reverse is definitely not true.
That being said, one specific Vulcan - Captain Solok from DS9 - WAS definitely deficient in that area. He was, in fact, deficient in the area of "not being an egotistical jackass".