Anyone know how Trump humiliated Merkel?
He openly slated Germany and especially BMW and Mercedes and their importing of cars to the USA he also said he would put a stop to that and impose huge taxes on them. He then scolded all NATO members and mentioned Germany again when saying they owe years of membership fees and should start paying their fair share. He also refused to commit to the Paris Agreement and he didn't mention Article 5 in his speech. Let's not forget he handed her an imaginary bill for NATO fees when she came to the White House and he flat out ignored her and refused to shake her hand for the cameras.
There are also (I would say extremely valid) rumours suggesting that Trump must have been extremely insulting in private to Merkel. It's said Trump must have offered her no assurances or given her any hope or confidence in anything he said for her to react the way she did in her speech that said Germany couldn't rely on the US anymore.
To say that Trump has pissed off lots of countries and their leaders over the last few days of his trip is putting it extremely mildly and underestimating it severely.