Where to wear the Glengarry??

[PiobBear]

Yes; uncover indoors (unless "under arms"; actively participating in a color or honor guard).

[Nanook]

Yes; uncover indoors

To remove a hat is submission and is driven the tradition of the person in their context within local custom but not exclusively by the rules of local custom. I would strongly refuse any request to remove my glengarry (when I'm wearing one).