RBF       
noun [ C ] US informal uk/ˌɑː.biːˈef/ us/ˌɑːr.biːˈef/
 天生臭脸(resting bitch face 的缩写)
abbreviation for  resting bitch face : an unkind, annoyed, or serious expression that someone has on their face when relaxed, without intending to
  Here are a few pointers for women accused of having RBF, and for anyone tempted to judge someone on this basis. 对于那些被指责天生臭脸的女性,以及那些试图以此来评判别人的人,这里有一些建议。 
 - More examples
 - I joined the ranks of a tribe of women who suffer from the scourge known as “resting bitch face” or, increasingly, just RBF.
 - When literally “at rest,” whether standing in the supermarket checkout line or zoning out during a meeting, RBF sufferers project a severe look of: “Don’t even think about talking to me.”
 - Here is a slideshow of celebrities who have RBF.
 - Chronically serious-looking faces - a “condition” recently dubbed “resting bitch face,” or RBF - is a maternal trait in my family.