Isn't it commonly showcasing adult Yankee senselessness? (7)
I believe the answer is:
inanity
'senselessness?' is the definition.
('inanity' can be a synonym of 'senselessness')
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for inanity that I've seen before include "Being silly" , "act of stupidity" , "Silliness in a tiny way" , "Mindlessness" , "Puerility" .)