Yes, Earn acts like baby in this episode, and everybody hates it. But is it the reason to dislike the episode?
In this episode Earn´s got money, Van is between jobs. But really, it just a few moments (episodes) back since Earn was the loser, and Van was being nice single mom treating him well, even though he was not worth it. Now, Van is beautyful, intelligent, responsible cool, understanding since EP01,(maybe too much so) and Earn comes out as an asshole here forgetting all that really fast.
Personally I have experienced this in real life, back and forth, me and her, so I find this episode to be realistic, and hurting, I like it.
The exaggeration of the German Polka Party setting is a comic tribute to the great actress Zazie Beats. She is half german, and has grown up in Germany. I, for my part, love actors that speak several languages (or fake it well), and I think she is great, and deserves more space.
So, I think it is only supercool that producers/directors chose to make this episode. And I wish that others liked it too..