Seriously.. that is so damn low. My friends and I have a regular system worked out where we use one person's weed one session, then mine the next, then someone else's the next time.. it's sort of like a community system.

But honestly... just be like, "Dude, you've smoked multiple 1/8ths of my herb, and I want you to chip in a few times just to be fair." If he doesn't go for it, just tell him that you don't want to smoke with him again. Mooching is rediculous.