For fanfic research purposes (wink) - what do you suggest is the best over-the-counter lube that a guy could use to jerk off with?

Silicone-based, not water-based..

stuff like Wet or Sliquid (or Astroglide X... regular Astroglide is *ugh* water/glycerin based) you can usually find in any city-based drugstore.. not so much in the boonies.

Have at it.