Most unattractive fib takes guts to spread round (7)
I believe the answer is:
ugliest
'most unattractive' is the definition.
('ugly' is associated in meaning with 'unattractive')
'takes guts to spread round' is the wordplay.
'takes' becomes 'lie' (I can't justify this - if you can you should give a lot more credence to this answer).
'to spread' is an anagram indicator.
'round' is an insertion indicator.
'guts' is an anagram of 'ugst'.
'lie' going within 'ugst' is 'UGLIEST'.
'fib' is the link.
This may not be correct. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for ugliest that I've seen before include "Most unpleasant" , "Least attractive" , "most unappealing" , "Most repulsive" , "superlatively unattractive" .)