silliest
sil-li-est
adjective
Superlative form of 'silly'; most foolish, absurd, or lacking good sense.
"That was the silliest excuse I've ever heard."
Thesaurus
Synonyms: airheaded, dizzy, featherbrained, lightheaded, light-headed, frivolous, empty-headed, giddy, silly, undignified, ridiculous, pathetic