Bananas are in it for sloth (7)
I believe the answer is:
inertia
'sloth' is the definition.
(inertia can mean laziness or sloth)
'bananas are in it' is the wordplay.
'bananas' indicates an anagram (informal term for mad).
'are'+'in'+'it'='areinit'
'areinit' is an anagram of 'INERTIA'.
'for' is the link.
(Other definitions for inertia that I've seen before include "Reluctance to change" , "Sluggishness - sloth" , "Lethargy" , "showing reluctance to move" , "I earn it (anag.)" .)