Cats are known for bringing dead mice/rats/birds and other vermin they may have found or killed in to their owner's home.

Upon meeting someone who is disliked, by using this phrase you imply that they are the vermin mentioned above.
(Upon meeting an ex-boyfriend at a party)
"Well well! Look what the cat dragged in!"
by Alpha_nine April 1, 2008
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An implication that someone is looking haggard, disheveled, and weather beaten...in very bad shape.
"Honey, don't I look fabulous in this new dress?"
"Look what the cat dragged in."
by Nick D March 10, 2005
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Describing someone or something who looks like a dead rat on your porch.
I was looking at Peewee's girlfriend and couldn't stop thinking, "Oh look what the cat dragged in!!"
by razzle dazzle 69 November 30, 2013
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