贔屓ひいきにする

expression, suru verb (irregular)

favor; be partial to; patronize

Used when someone shows unfair preference or special treatment toward a particular person, group, or establishment. Often implies bias or favoritism, but can also simply mean being a regular customer.

• 先せん生せいは特とく定ていの生せい徒とだけをひいきにしている。

  The teacher favors only certain students.