a cheap shot
US /ə tʃiːp ʃɑt/
UK /ə tʃiːp ʃɑt/

1.
coup bas, attaque facile
an unfair or unsporting remark or action, especially one made against a vulnerable person or at an opportune moment
:
•
His comment about her past mistakes was a cheap shot.
Son commentaire sur ses erreurs passées était un coup bas.
•
The politician took a cheap shot at his opponent's family.
Le politicien a fait un coup bas à la famille de son adversaire.