Skinny people plan to mingle with obese (9)
I believe the answer is:
beanpoles
'skinny people' is the definition.
(I've seen this before)
'plan to mingle with obese' is the wordplay.
'to mingle with' indicates anagramming the letters (letters mix and mingle around).
'plan' with its letters anagrammed with 'obese' makes 'BEANPOLES'.
(Other definitions for beanpoles that I've seen before include "Tall and thin people" , "skinny people" .)