[Nagoyankee]

You're driving me crazy, munzy! Send me some tiramisu right now so I could clam down!

Look at this ---> 王子たるもの部屋着はバスローブ（王宮にいる時

It doesn't have a verb!

That's why he puts one (です) in the following phrase, which is もしくはadidasです.

王子たるもの部屋着はバスローブ（王宮にいる時）, もしくはadidasです. <-- Now you have a sentence. Its subject is 部屋着.

He's saying "部屋着 is either A or B."