Dignified expression of unhappiness regarding upset (5)
I believe the answer is:
sober
'dignified' is the definition.
(sober can mean dignified or solemn)
'expression of unhappiness regarding upset' is the wordplay.
'expression of unhappiness' becomes 'sob' (I can't explain this - if you can you should believe this answer much more).
'regarding' becomes 're' (re can mean regarding, concerning).
'upset' is a reversal indicator.
're' reversed gives 'er'.
'sob'+'er'='SOBER'
Can you help me to learn more?
(Other definitions for sober that I've seen before include "Dignified -- lacking colour" , "Temperate" , "Earnest" , "Sedate and rational" , "Serious; muted in colour" .)