Leader of men is boss in funny business? (8)
I believe the answer is:
mischief
'funny business?' is the definition.
'leader of men is boss' is the wordplay.
'leader of' indicates taking the first letters.
'boss' becomes 'chief' ('chief' can be a synonym of 'boss').
The first letter of 'men' is 'm'.
'm'+'is'+'chief'='MISCHIEF'
'in' acts as a link.
(Other definitions for mischief that I've seen before include "Playful misbehaviour" , "Devilment, impishness" , "Wrongdoing, devilment" , "Playful troublemaking" , "Black . . . . . . . . (Evelyn Waugh)" .)