I was reading about Jellyfish recently -- which aren't really fish, but plankton -- and found one thing in particular rather...fascinating: Their mouth is also their anus.
As soon as I read this I thought of a couple of people I know who also have this "condition". So now calling someone a jellyfish does not only refer to their spine-less personality, but can also mean they are good at spewing crap when they talk. I assume this also means that jellyfish have bad breath, and don't kiss on the mouth much :-)