Whatever racehorse I’m on in horsing around! (4,4,2,5)
I believe the answer is:
come rain or shine
'whatever' is the definition.
I don't know anything about this answer so I can't judge whether it can be defined by this definition.
'racehorse i'm on in horsing around' is the wordplay.
'horsing around' is an anagram indicator (I've seen 'horses around' mean this).
'racehorse'+'im'+'on'+'in'='racehorseimonin'
'racehorseimonin' with letters rearranged gives 'COME RAIN OR SHINE'.
Can you help me to learn more?
(Other definitions for come rain or shine that I've seen before include "no matter what the circumstances may be" , "regardless of circumstances" , "Whatever the weather" , "Whatever the circumstances" .)