Dog tired (sometimes written as dog-tired) is an English expression used to describe a state of complete exhaustion, when someone hasn't got the energy to do anything else.
The dog in the picture below is clearly dog-tired, as he has fallen asleep in the middle of eating!
Where does the expression 'dog tired' come from? Do you know?
Post a comment if you know the answer, or would like to make a guess :-)
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