I gave programming examples because of the HN crowd here. In my own life, it varies quite a bit. In the past week, topics have included:
* Fluorescence. (At a cocktail bar full of blacklights. Any cocktail containing tonic glowed due to the quinine.)
* Comparing the stories of Alistair Reynolds and Lawrence Watt-Evans. Their fans seem to overlap quite a bit, even though their genres are different.
* Beard growth. Why most militaries don't let soldiers grow beards. (Beards prevent gas masks from sealing well.) How fast beards grow. (About 5 nanometers per second, hence the beard-second as a unit of measure[1].)
* Noticing that dentists can replace teeth, but doctors can do little for chronic back pain.
* Laser interferometer microphones.
1. http://en.wikipedia.org/wiki/List_of_humorous_units_of_measu...