After learning about the German business culture, Jack should avoid...

In the context of German business culture, using humor may not be well received, particularly in formal or initial business interactions. Germans typically value professionalism and seriousness in business dealings, and humor can sometimes be perceived as unprofessional or inappropriate. While humor can be an effective way to build relationships in some cultures, in Germany, it is usually better to err on the side of formality until a more casual rapport has been established.

Other aspects of German business etiquette, such as the use of titles and shaking hands, are important and demonstrate respect for hierarchy and formality. Making eye contact is also seen as a sign of confidence and sincerity in communication. Therefore, while Jack should maintain a respectful demeanor and approach in these areas, humor should be approached cautiously, especially in more serious business settings.