tralala

Tralala is a playful vocalization representing a carefree melody or humming, often used to suggest lightheartedness, nonchalance, or dismissiveness.

It mimics the sound of someone singing without words, typically in a lilting, repetitive pattern.

The term can appear in writing to convey that someone is blithely unconcerned or going about their business without worry: She walked in, tralala, as if nothing had happened.

It sometimes carries a mocking or ironic tone.