Siendo mas claro con las variables en el admin

lists/admin.py

@@ -4,18 +4,24 @@ from lists.models import Tag, Entity, ListItem, OpinionHelpful
 
 @admin.register(Tag)
 class TagAdmin(admin.ModelAdmin):
-    pass
+    list_display = ('pk', 'name', 'username')
+    list_filter = ('user', )
+
+    @staticmethod
+    def username(obj):
+        return str(obj.user.username)
 
 
 @admin.register(Entity)
 class EntityAdmin(admin.ModelAdmin):
-    pass
+    list_display = ('pk', 'entity_type')
+    list_filter = ('entity_type', )
 
 
 @admin.register(ListItem)
 class ListItemAdmin(admin.ModelAdmin):
     list_display = ('pk', 'username', 'entity_mbid', 'stars')
-    list_filter = ('stars',)
+    list_filter = ('user', 'stars')
     filter_horizontal = ('tags', )
 
     search_fields = ['pk', 'user__username', 'entity__mbid', 'stars']