Likes ...
JANitors
APRicots
MAYors
caJUNs

JULiet
dAUGhters
SEPia
OCTopuses

NOVels
siDECars

But Dislikes ...
custodians
nectarines
governors
Creoles

Romeo
sons
beige
jellyfish

sonnets
cabooses

My friend likes words that contain three consecutive letters that
are the abbreviations for the months of the year (JAN, FEB, .. DEC).

The three state capitals he will also like are Bismarck (MAR),
Juneau (JUN), and Augusta (AUG).