laugh over (someone's) shoulder

Translations
смеяться за (чьей-либо) спиной
He felt like his colleagues were laughing over his shoulder.
Ему казалось, что коллеги смеются за его спиной.
Definitions
To laugh in a way that is directed at someone, often behind their back or without their knowledge, typically implying mockery, ridicule, or gossip about that person.