Can you get hep b if you share for example a cup of tea with an infected person?

Hepatitis B: Highly unlikely. Hep B is a bloodborne virus and transmission from an infected person to someone else requires some exchange of blood. If the person drinking the tea had an open mouth sore and traces of blood got into the tea, there might be some risk to you, but this scenario seems unlikely. Do not, however, share toothbrushes, razors, etc. that could be contaminated with blood.