When exiting a country (Hong Kong in this case) it seems that Lady Gaga likes to stay under the radar. Literally, if you assume her headgear was inspired by radar displays and receivers.
>> Scroll down to see the promo for Lady Gaga's Simpsons appearance!
Unfortunately for the be-hatted one, she has already set the bar rather high for herself in terms of hats whose circumference = pi x d thanks to that performance at the MTV European Music Awards (see below):
We'll just file this under 'business casual'.
You can see a more classic selection of bonkers outfits in The Simpsons trailer below: