那“社恐”用英语该咋说呢？
可以说成“introvert”，英文释义：someone who is shy, quiet, and unable to make friends easily.
害羞、安静、不容易结交朋友的人，也就是性格内向者。
反之则是“extrovert”，英文释义：an energetic happy person who enjoys being with other people.
精力旺盛、开心活泼的喜欢与人交往的人，也就是性格外向的人。
举个例子：
This group included a minority of students who were quite introverted and shy, and others who whilst much more extrovert were not necessarily always naturally cooperative.
这一群体包括少数性格内向、害羞的学生，还有一些性格外向、天生不会合作的学生。
除此以外，互联网上还衍生出“textrovert”，指的就是在网上能言善语，但是现实生活着内向安静的那一类人。
社恐还可以说成“wallflower”，英文释义：
a shy person, especially a girl or woman, who is frightened to involve herself in social activities and does not attract much interest or attention.
害怕融入社交活动中，不会引起太多兴趣或关注的害羞的人，尤其是女孩子，也就是壁花，尤指社交活动中无人青睐的害羞女子。
举个例子：
Sooner or later someone would take pity on the poor wallflower and ask her to dance.
迟早会有人可怜那个没有舞伴的害羞姑娘，请她跳舞的。