1) Is calling someone else god just for fun would be considered shirk even tho we don’t mean it? For e.g sometimes people say "I worship him" or addressing myths like "Zeus the god of sky"

2) Are all non Muslims committing shirk since they don’t believe in Allah? Will they be punished for that?

by

1) One should definitely avoid that kind of talk even if it is jokingly.

Sayings about what other people believe like the belief in Zeus is a different issue. You are saying what they are believing in not what you are believing.

2) Shirk is associating a partner with God. That means believing in other Gods. Anyone who fits in that category is a mushrik.