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be as dull as dishwater
To be very boring or unexciting. This phrase is often used to describe a person. My date with Dave was not great—he is as dull as dishwater. I fell asleep during that movie because it was as dull as dishwater.
*dull as dishwaterand *dull as ditch water
very uninteresting. (*Also: as ~.) I'm not surprised that he can't find a partner. He's as dull as dishwater. Mr. Black's speech was as dull as dishwater.
be as dull as dishwater/ditchwater(informal)
to be very boring He loved the book but I thought it was as dull as ditchwater.
dull as dishwater
Boring, tedious, as in That lecture was dull as dishwater. The original simile, dull as ditchwater, dating from the 1700s, alluded to the muddy water in roadside ditches. In the first half of the 1900s, perhaps through mispronunciation, it became dishwater, that is, the dingy, grayish water in which dirty dishes had soaked.
(as) dull as dishwater
mod. very dull. Life can be as dull as dishwater.