hmmm ... i am the same as some pple on here ... its oky if I say/call kikko a rat (i prefer the word monster.. haha .. IMO he could never look like a rat) or someone i alreayd know and know that they meant it in a joking manner...
but if a stranger said that, i would be peeved... prolly ask them politely and in a joke/cute way (buuut isn't it like 90% of a joke is the truth .. some number iunno) to not refer them to a rat and proceed with the conversation.
however, if your sister's neighbor wants one, why would she refer to something that she wants a rat? so i don't think she meant any harm. but you prolly got mad b/c i'm sure its not the first time that's happened to you and it was an automatic response .. b/c we've all encountered those pple who really DO mean it when calling our babies 'rats'... so its understandable you know? so don't worry about it.