Shabby detective I went out with, necking drink (11)
I believe the answer is:
dilapidated
'shabby' is the definition.
(I've seen this before)
'detective i went out with necking drink' is the wordplay.
'detective' becomes 'di' (Detective Inspector abbreviation).
'went out' becomes 'dated' (dating is a kind of going out).
'with' means one lot of letters go next to another.
'necking drink' becomes 'lap' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'i'+'dated'='idated'
'idated' put after 'lap' is 'lapidated'.
'di'+'lapidated'='DILAPIDATED'
Can you help me to learn more?
(Other definitions for dilapidated that I've seen before include "shabby" , "Broken-down" , "uncared for" , "Broken down and falling to bits" , "Run-down, neglected" .)