silly grin

Translations
глупая ухмылка
He had a silly grin on his face after the joke.
У него была глупая ухмылка на лице после шутки.
Definitions
A silly grin is a broad, often goofy smile that conveys a sense of playfulness or lightheartedness, typically characterized by an exaggerated or whimsical expression.
Words
grin

noun
усмешка
silly

adjective
глупый