Frivolous

ветреный

vetrenyj

(silly; especially at an inappropriate time or in an inappropriate manner)

легкомысленный

lexkomyslennyj

(silly; especially at an inappropriate time or in an inappropriate manner)

нева́жный

nevážnyj

(of little weight or importance; not worth notice)

незначи́тельный

neznačítelʹnyj

(of little weight or importance; not worth notice)

несерьезный

neserʹjeznyj

(silly; especially at an inappropriate time or in an inappropriate manner)

пове́рхностный

povérxnostnyj

(silly; especially at an inappropriate time or in an inappropriate manner)

пустяковый

pustjakovyj

(of little weight or importance; not worth notice)