Cracked like cracknel? (5)
I believe the answer is:
nutty
'cracked' is the definition.
(synonyms)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for nutty that I've seen before include "Like, eg, brazils" , "Eccentric - like nougat?" , "Mentally unhinged (slang)" , "like vegetarian roast?" , "Like cobs, brazils, etc" .)