You ever looked into autism much? Sounds a lot like sensory overload to me.

Might be worth discussing this with a therapist.

I’ve recently become aware that I do the same thing. While I’m still pretty awkward in 1 on 1 conversations, I mostly do fine. But just add one other person and I shut down. It’s like I don’t know how the conversation is supposed to work so I try to take myself out of it.

Yes there is but it's not as well studied. You can see a difference in social skills between adults who were homeschooled during elementary school, and adults who went to public/private elementary schools.

But social skills can also be partially genetic, certain traits of the Big 5, including Extroversion, can be geneticly passed down from parents.

Or you might have mild autism which is also common.

Holy shit you've just described me to a T. Shutting down when it's more than two people in the group, but being sociable one on one. The alcohol and weed dependance to be fluid in social situations, though this has opened up the door to abuse in the past.

I find it bizarre that I can walk away from a social situation knowing immediately what I should have said in that moment, and yet I always tend to say the wrong thing, almost like my shutdown brain takes over and lowers my IQ by 50 points. But then the cloud lifts as I walk away.

It's really difficult, but it really makes me happy knowing I'm not the only one it seems. Do you have ADD, by chance?

Nah, while we do get a lot of practice regarding social skills during kindergarten/early school years it isn't a critical period. Anyone can, unless hindered by mental illness, achieve decent social skills even if they start out as extremely socially awkward and/or shy.

I for one was bullied through all my school years and barely even had a friend, much less a good friend. I couldn't handle social situations at all, literal dread and nausea even thinking about them. But in my 30s I decided to change myself, I moved far away and tried to start a new fresh life. And I managed! Slowly but surely I could socialise more and nowadays its easy, even public speaking feels doable (formerly impossible). The fact that no one knew me allowed me to "fake it until you make it" and slowly but surely learn, train and conquer, basic social skills.

You seem like are describing dissociation/numbing out as a result of a stressful situation - your brain goes into fight or flight mode, is scared, and shuts down a lot of your processing. The fact that it happens when more people are present is likely tied to a over-sensory issue or a trauma.

It is often a symptom or sign of one of the following: C-PTSD, autism or ADHD (which are often comorbid so harder to tell which the symptom is tied to).