What one thinks about a bad side (5)
I believe the answer is:
ideas
'what one thinks' is the definition.
I can't judge whether this defines the answer.
'about a bad side' is the wordplay.
'about' is an insertion indicator.
'bad' indicates anagramming the letters.
'side' anagrammed gives 'ides'.
'a' placed within 'ides' is 'IDEAS'.
Can you help me to learn more?
(Other definitions for ideas that I've seen before include "Fancies" , "Thoughts or opinions" , "Thoughts, personal views" , "Notions, concepts" , "Thoughts from Sadie" .)