In Germany, public nudity is accepted in some situations. Most public parks allow nude sunbathing. However, undressing in a lobby
, rather than a restroom, is a bit much. That was very careless. Travelers should know the local customs ahead of time instead of just making assumptions base on their own cultural experiences.
In North America, it would just be a warning in most cases, a fine if the warnings are ignored, & jail for repeated offenders. There are many websites where men post photos of their wives/girlfriends posing nude in public places. Some posters mention that they've been caught by authorities & just got a warning or had to go to court & pay a fine. None mentioned any jail time. Such European sites are more abundant & the posers more audacious. http://www.nude-in-public.com/