FATUOUSLY
fatuously, inanely
(adverb) vacuously or complacently and unconsciously foolish
Source: WordNet® 3.1
Etymology
Adverb
fatuously (comparative more fatuously, superlative most fatuously)
With smug stupidity or vacuous silliness; idiotically.
Synonyms
• (with smug stupidity): foolishly, idiotically, stupidly
Source: Wiktionary
FATUOUS
Fat"u*ous, a. Etym: [L. fatuus.]
1. Feeble in mind; weak; silly; stupid; foolish; fatuitous. Glanvill.
2. Without reality; illusory, like the ignis fatuus.
Thence fatuous fires and meteors take their birth. Danham.
Source: Webster’s Unabridged Dictionary 1913 Edition