Add fuel to the fire
Criticism that makes a situation worse.

Backseat driver
Someone who criticizes from the sidelines, without being directly involved.

Take it with a grain of salt
To not take criticism too seriously.

Bite the hand that feeds you
Criticizing someone who helps or supports you.

Sitting on the fence
Avoiding criticism by not taking sides.

Throw under the bus
Criticizing or blaming someone to protect oneself.

Shoot the messenger
Criticizing the person who delivers bad news.

Hit below the belt
Giving unfair or hurtful criticism.

Monday morning quarterback
Criticizing with the benefit of hindsight.

Put someone down
To criticize someone harshly and belittle them.

Point the finger
To blame or criticize someone.

Break someone's heart
To deeply criticize or hurt someone's feelings.

Run someone down
To criticize someone unfairly.

Pick holes in something
To find faults in something and criticize it.

Firing on all cylinders
To criticize with full force or intensity.

On thin ice
Being in a situation where any action might lead to criticism.

Nail to the wall
To criticize or punish someone harshly.

Ruffle someone's feathers
To upset someone with criticism.

Split hairs
To make overly detailed criticisms about minor things.

Take the heat
To accept strong criticism.