There have been studies conducted (and I don't have the links handy, but Google can find them)... one in particular was performed at the University of Kentucky... Nicotine is absorbed rapidly into skin, and even faster into the soft tissue of your mouth, tongue, and lungs. The hotter the vapor and the longer you hold it before exhaling (along with how deep you draw the vapor into your lungs) will factor how much you retain, and how much you exhale. Just remember, you are still absorbing it until it leaves your lips or nose. That being said, the best estimates (low and high) from the University study showed 70% absorption for mouth-only drag and quick exhale. Full lung-hits with a few seconds of holding it... resulted in 98%+ absorption.
NOW... 2% upon exhale... distance of several feet to another person, air-currents, blah, blah, blah... you'd get more nicotine from eating a potato, tomato or eggplant than from second-hand vapor! Yes, Nicotine exists in EVERY fruit/vegetable in nature... it is a natural defense against insects.
I agree he should be more considerate of others, but rest-assured you WILL NOT get cancer, COPD, asthma... or anything else from breathing second-hand vapor... and you WILL NOT become a nicotine addict from breathing second-hand vapor either