Grinning like a shot fox
Australian SlangDefinition
Wearing a broad, self-satisfied, slightly sly grin; looking very pleased with oneself.
Examples
"After nailing the job interview, he walked out grinning like a shot fox, already planning celebratory beers."
"She pulled off a sneaky bargain at the markets and came back grinning like a shot fox."
"When our team pinched the win in the final seconds, the captain was grinning like a shot fox in the team photo."