Meaning:
“社交” means “to socialize,” “牛人” means “genius, badass,” and “症” means “syndrome.” A derivative of the term “社交恐惧症” (shèjiāo kǒngjù zhèng, meaning “social anxiety disorder”), this phrase coined by Chinese netizens refers to those who are extremely self-confident and extroverted in social occasions. For instance, this kind of person is willing to talk to strangers, crack jokes and naturally draws a lot of attention at social functions.
Example:
A: 昨天小李开轰趴，你去了吗？
Zuótiān xiǎolǐ kāi hōngpā，nǐ qù le ma？
Did you go to Xiao Li’s home party yesterday?
B: 没有。他的朋友大都有社交牛人症，那样的场合我有点儿不自在。
Méiyǒu。Tā de péngyou dàdōu yǒu shèjiāo niúrén zhèng，nàyàng de chǎnghé wǒ yǒudiǎnr búzìzài。
No. Most of his friends are extremely extroverted and I feel a bit awkward in those occasions.