@maj some mermaids have a little butt bump! I think it's more common when the mermaid is represented by a human actor wearing a costume tail, so their curves show under the costume.
So, with all this, do I think that mermaids are sexy? Well, anything that makes me think this much is pretty intriguing, so I'm going to go with Yes, but. Thanks to everyone who replied or responded to the poll.
I mentioned earlier in the thread that there's another thing about some mermaids, like in "The Little Mermaid" or "Splash": they can develop regular human legs when they are on land. It seems unfair to say that mermaids are sexy, but only when they're not in their half-fish form.
There's also the notion that sailors developed the idea of mermaids from seeing pinnipeds like seals or manatees from far away, and with a bit of longing and loneliness thrown in. I think it is far-fetched to suppose that people who live by the sea would be unfamiliar with everything that lives in the water. I don't think a sailor would not know what a seal looks like.