Rat

hi..
what do we mean when we say..
1.someone was nicknamed as a "desert rat". and...
2.lambasted someone a "love rat".

thank you for your help.

You are, no doubt, talking about the slime that did the tell-all book about Diana, Princess of Wales. He's a "rat" because he is a low vermin-like creature. "Desert" because, according to an article, he was "a tank commander in the 1991 Gulf War."