"idle, meaningless talk," 1918, probably echoic; the adjective meaning "bland, dull" is from 1919, perhaps influenced by French blasé "bored, indifferent." The blahs "depression" is attested by 1966.
权威例句
1. How can you build socialism if you just blah - blah and don't do a stroke of work?
成天磨嘴皮子不干活,还能建设好社会主义?
2. There he goes , blahblahblah, talking nonsense as usual.