Donald Trump has married two European women; so he is very well-versed in how to press the right buttons to get the outcome he wants, and he certainly played Angela Merkel into making more than just a fool out of herself:
That is the look of an admission that she has no control. She is trying to gain it, or even re-gain it, but she has no power here. Zero.
This is the Ineffectual Mom Stare that makes up about 99% of all Dr. Phil episodes. Mom gives the Icy stare -- if she had any control or power, it would be unnecessary to shoot a dirty look -- and Dr. Phil then promptly chastises Ineffectual Mommy, accusing her of being weak, passive, and neglectful to the point of being an Abusive Mommy.
Cue in audience applauding. Yay, you tell that Ineffectual Mommy off, Dr. Phil!
What did the stare accomplish? Not a thing. Trump still did what he wanted, threw the Photo Op meeting down the drain, and then jetted off to a cooler and more historic meeting, leaving Ineffectual Mommy to eat his dirt.
Merkel has no power. She cannot command a room of her peers. She has the majority on her side -- Trump has himself, and he wins that battle because he doesn't need an entourage to validate him.
Merkel has messed up back home, and she would have been kicked to the curb a long time ago if she didn't cultivate an image of being able to hold her own with other foreign leaders.
Now that she lost face by stooping to having a staring contest with a man who won it, she is inert as a political force. She could not predict Trump, and she had plenty of time to do it. She could not control or persuade him.
If she cannot handle a simple feel-good Photo Op meeting, she cannot be expected to negotiate any sort of beneficial deal for the German people in places where it actually counts.
She has been infantilized and neutralized, becoming a butt of jokes. A stare only works if you have cards to play -- and the fact that she doesn't makes that stare worthless...