I totally understand. For me, others might find me selfish, but I NEEEEEEEED my alone time, my privacy, my separate space. And I have trouble with boundaries, too, which makes for bad situations sometimes. I don't know how to make it sound sweet. "I'm very sorry, but I just can't give rides anymore - I really need to just get straight home." And straight to work worrying only about my own schedule. If you want to make stuff up, you can also say it's to be able to run errands, go to some class, etc - but I"m trying not to be "polite" by adding on anything extra, I need to just close my mouth as soon as possible to keep it simple. But really - you need to be able to just deal with your own schedule, it is not easy to balance work and life as it is without having to add someone else's schedule to your balancing act.