be as dull as dishwaterbe as dull as dishwater/ditchwater
informal to be very boring.
He loved the book but I thought it was as dull as ditchwater.
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.