One who is uncontrollably awkward in social situations. This person, in normal everyday life, may seem rather normal, but when thrown into a social situation, the person is suddenly petrified, unable to speak or act in any way that is not completely uncomfortable for all who bear witness. This syndrome is sometimes hereditary, though typically develops in preteen years and lasts through adulthood. Not to be confused with an actual mental handicap.
"The strangest thing has been happening to me lately," said Shauna. "I'll be completely fine one moment, and when I enter a social situation, I suddenly can't act or speak in any way that is not completely uncomfortable and humiliating."
It's not a mental illness, I think you have been struck by the SAS (Social Awkwardness Syndrome)!" Said Susan. "It affects one in every three adults, and targets those who work in corporate settings, especially stock exchanges.