Tuning cars may bore some people, but if you are looking for a way to simply kill time, it's got my vote. If you are anything like me, you have hundreds of cars in your garage which you have not spent much time behind the wheel... maybe a quick race or two after buying, upgrading and tuning them but no real "seat time" to speak of. And remember, for each car you can save 3 different custom tunes in the settings screen (look for tabs A, B, C), and also you can custom-name each tune -- I have started doing "long track," "short track" and "endurance race" tunes (I don't drift, yet). On that note, why not spend some time practicing your drifting technique? Or practice manual shifting if you aren't already a master? And of course you can always gift a car to one of your friends if you are feeling generous.
Other suggestions: get some exercise, watch a movie, go on a date, take a nap, try a new recipe, call a friend or family member you haven't talked to in a while, do some yardwork, rearrange the furniture, do some laundry... I can think of a thousand things to do with spare time.
I've just been very board lately and have nothing to do.
