Mom look is the look you get when your boyfriend/girlfriend introduces you to their mom and you see the look of disapproval in her eyes.

Mom look指你男/女朋友把你介绍给他/她妈妈时，你从对方妈妈脸上看到的不满的表情和眼神。我们称为“老妈表情”。

For example:

-I think my mom really likes you.....

-Uhhh, no. She totally gave me the mom look....I feel so ashamed.

-我觉得我妈挺喜欢你的…

-才不是呢，看看她的表情就知道了，我觉得好丢脸。