Well, that's more understandable. With that said, be warned, it's almost impossible to completely remove the smell of smoke from yourself to the point where a non-smoker in close proximity won't detect it.

Your best bet is still to wash your hands/face, air yourself out on the drive home, and apply febreeze.

Your next problem will be that they are suspicious of why you reek of Febreeze.

All in all. Your best bet is honesty if you're 18 and to not smoke if you're underage.