Hello Olga:
I was not entirely clear on the definition, although I have a general understanding of the phrase.
I found a website which indicates:
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"1. Socially Retarded
An incurable disease that the carrier is unaware of possessing and which causes uncontrollable shedding of relationships. Symptoms include:
1: The inability to comprehend the subtleties of conversation.
1a: Hijacking conversations, discussion threads or wall posts that the individual is not involved in with comments not related to the subject of discussion."
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.
Please understand that the definition given above is a sort of humorous definition.
It basically tells us that a SOCIALLY UNAWARE person has no respect for social conventions, common courtesy, or being "on topic" and is generally irrelevent to other people's dialogues.
I have rather coined a term that I find expresses something of the same.
I refer to certain kinds of people as SOCIAL PRIMITIVES.
---Warm Regards, Bruce