Irate, Sir? Bats? They're seldom seen (8)
I believe the answer is:
rarities
'they're seldom seen' is the definition.
'irate sir? bats?' is the wordplay.
'bats?' indicates anagramming the letters (slang for mad).
'irate'+'sir'='iratesir'
'iratesir' anagrammed gives 'RARITIES'.
(Other definitions for rarities that I've seen before include "Curios" , "Is a trier for scarce things" , "Uncommon things" , "collector's items" , "Things seldom encountered" .)