Pat middle-men on the head! (4)
I believe the answer is:
pate
'the head' is the definition.
(humorous term for the head)
'pat middle-men on' is the wordplay.
'middle' means to look at the middle letters.
'on' says to put letters next to each other.
The middle of 'men' is 'e'.
'pat'+'e'='PATE'
(Other definitions for pate that I've seen before include "Tasty meat paste, maybe de foie gras" , "Meat paste, may be de fois gras" , "Tape around tasty meat paste" , "chef's preparation" , "Posh 8" .)