Billionaire into S&M rejected seedy things (6)
I believe the answer is:
melons
'seedy things' is the definition.
(they have seeds)
'billionaire into sm rejected' is the wordplay.
'billionaire' becomes 'Elon' (tech billionaire Elon Musk).
'into' is an insertion indicator.
'rejected' says the letters should be written in reverse.
'sm' written backwards gives 'ms'.
'elon' inserted within 'ms' is 'MELONS'.
(Other definitions for melons that I've seen before include "Fruits with hard rinds" , "Lemons turn out to be other fruits" , "Juicy fruit" , "Juicy fruits" , "Lemons make other fruits" .)