The poor, portly manatee, having to endure this gibe time and again: "The early explorers thought manatees were mermaids. Guess they'd been at sea a little too long!"
Local tour guides have their own versions of the line and the Internet offers dozens more.
Even an estimable literary journal, The Believer, lampooned recently that the female Florida manatee's tail, forelimbs and "prominent nipples" make it "a likely progenitor of the mermaid myth; however, the manatee face -- jowly, with the bone structure of a sock puppet -- compounded by a 2,000- to 3,000-pound body -- declared distinctly more minivan than mermaid in shape analysis studies -- challenges the notion of manatee as marine temptress."
Any seafarer attracted to a manatee, that author concluded, must have been delusional from rickets.
Manatees as mermaids? C'mon.
But historians, folklorists and scientists say it's no joke at all.
The order Sirenia, to which the Florida manatee belongs, is from the Latin siren, or mermaid. The myth of a part-woman, part-fish with great seductive powers -- and no scruples -- has existed for centuries. As long as there have been seafarers, it seems, there have been mermaids to mess with their minds.
The mermaid has occasionally been depicted in writing and art as ugly, but she is more often pretty, if a little lewd. In her brashest incarnation she sings loudly and hoists her split tail around her head, like some tantric yogi -- a far cry from Disney's doe-eyed and marriage-minded Ariel.
"Usually these legends of singing sirens were made by sailors as explanations for why they were led astray," said Natalie Underberg, a folklorist at the University of Central Florida.
The New World sirens were a gentler, if homelier, lot.
Sailing near the Dominican Republic in 1493, Christopher Columbus described in his log some "female forms" that "rose high out of the sea, but were not as beautiful as they are represented." They did not, it's worth noting, wreck his ship.
Anthony Piccolo, a professor of literature at Manhattanville College in Purchase, N.Y., said Columbus was mentally primed for mermaids when he saw what history holds to be manatees. Folklore and early travelers' tales featured mermaids aplenty, and the old maps of the known world, including those Columbus consulted, "were always fringed with mermaids and monsters."
In 1614, English explorer John Smith claimed to have seen a mermaid in the Caribbean, and was more impressed than his Italian forebear.
"Her long green hair imparted to her an original character by no means unattractive," he wrote in his log, adding that he'd "begun to experience the first effects of love," when the mermaid turned over and revealed her fish parts.
Even present-day observers have discerned human attributes in sea cows. In the 30 years that James Powell, a biologist with the Wildlife Trust in St. Petersburg, has worked with manatees, "there have been times when they come up out of the water and the light has been such that they did look like the head of a person."
"If you were expecting to see a mermaid," he said, "you'd see this back and tail come up with no dorsal fin" -- as many mermaids are drawn.
Piccolo said manatees would have appeared only more human, and enticing, to New World explorers. The Age of Exploration was also the age of Peter Paul Rubens, the Flemish painter of voluptuous models. The female ideal was much heavier then, and "deprivation of intimacy inflamed all these voyages," Piccolo said.
"Anything in the water became a projection of the sailors' need for contact."
The sailors were deprived in other ways too.
"Some were near their deaths from hunger. It's incredible to me how human beings could endure the extremes on these voyages ... when you see the ship Columbus used, it's like a little pot," Piccolo said, without heat, fresh food or anything resembling comfort.
Some of these sailors apparently conflated their desires for food and for intimacy, seeing both possibilities in the Rubenesque manatee.
In 1789, a Scottish magazine reported that the crew of the Halifax, sailing in the Caribbean, had caught and killed several, and that they tasted like veal.
In this day, manatees probably wouldn't be the first choice of seagoing creatures to represent mermaids," Piccolo said, and not just because slender figures are in fashion.
"I don't think the contemporary imagination is fueled with myth," he said, and sex "is seen as a land activity" that only ever entered seafaring lore because the voyages were so long, miserable and sex-deprived.
Which also helps explain why passengers on today's cruise ships so seldom spot mermaids.