Flatter all but me and Jack (3)
I believe the answer is:
tar
'jack' is the definition.
(both are informal terms for sailor)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for tar that I've seen before include "Thick, sticky liquid distilled from coal" , "Sticky cigarette residue" , "Familiar sailor - what a rat" , "Viscous bituminous substance" , "Product of smoking cigarettes" .)