Glass.
Shia Labeouf mode ACTIVATE: "NononononoNONONONO!"
(And yes, glass is technically a liquid; slowest moving liquid known to man.)
Solid glass at room temperature is not a liquid at all, Pitch/Bitumen is the slowest-moving liquid known to man (about 230,000,000,000x as viscous as water).
Just to make it easier, if you think of a solid or a gas, it will be in its molten/liquid state, and your mouth/body will be at liquification pressure and temperature (which is usually enough to kill you in most cases).