I'm always fascinated by those lottery machines in which you open a tube, and a numbered ball shoots up. It's like magic, as far as I'm concerned. Of course, it's also bad for my wallet...
And I'm also madly in love with lava lamps. As, I think, we all are. And if you aren't, you should be, you
AND I'm fascinated with coming up with novel ways to swear at people.
So why not combine the three?
This Lava Lamp would have a shorter chamber than standard lamps to prevent too much heat loss. At the top of the chamber would be a set of 17-segment displays (like 16-segment displays, but with the addition of a dot at the bottom for punctuation). Rather than LEDs, these would basically consist of hinged flaps, which can create all 26 letters, numbers 0-9, and basic punctuation (! ? .)
By entering data into a keypad, these hinged flaps would open, allowing heated lava to flow into the spaces through a tube in the bottom, spelling out characters as necessary.
To prevent clogs, the spelling mechanism would have a higher specific heat than the wax or matrix, allowing the wax to remain heated and eventually pour out as the lamp is turned off.
To change spelling while the lamp is still on, simply press a "Clean" button on the keypad or lamp body, which would reduce the power, and therefore heat, of the lamp several degrees for several minutes, allowing the wax to pour out of the (still warmer) spelling mechanism and back into the matrix.
For simplicity, this could simply use a standard USB keyboard.
EDIT: Thanks to [half] for the link explaining what the hell those displays are called.