Hydrofluoric acid, though I don't think it melts your bones in a dramatic/fast way. It seems to be partially so dangerous because it doesn't "burn" right away, and as you say, is absorbed quickly in skin. So you might not rinse it off quickly.
"Piranha solution" (sulfuric acid, water, and hydrogen peroxide) is closer to what tv/movies portray hydrofluoric acid being like. That is, being able to disappear a body in it.
> It seems to be partially so dangerous because it doesn't "burn" right away, and as you say, is absorbed quickly in skin. So you might not rinse it off quickly.
It seems to be dangerous in a lot of different horrible ways. It's always fun reading an MSDS for substances like this: https://www.airgas.com/msds/001077.pdf
"Piranha solution" (sulfuric acid, water, and hydrogen peroxide) is closer to what tv/movies portray hydrofluoric acid being like. That is, being able to disappear a body in it.