Untidier disturbed individual? That's right! (7)
I believe the answer is:
messier
'untidier' is the definition.
('messy' can be a synonym of 'untidy')
'disturbed individual? that's right' is the wordplay.
'disturbed individual?' becomes 'mess' (I can't justify this - if you can you should give a lot more credence to this answer).
'that's' becomes 'ie'.
'right' becomes 'R' (common abbreviation).
'mess'+'ie'+'r'='MESSIER'
Can you help me to learn more?
(Other definitions for messier that I've seen before include "comparatively untidy" , "Less organised" .)