Look what the cat dragged in!
形容一個人或東西污穢不堪的狀態

explanation :  This folksy expression is said about someone or something that looks messy, dirty or in worse than normal condition.  If a child comes into a house with mud and stains on his clothes, the mother might say "Look what the cat dragged in!".  This expression should only be used with friends, since people might get offended if you say it and don't know them!