i bet your sister is letting that douchebag joyride the $hit out of your car, doing donuts and seeing "just how fast it will go"
if you are paying the monthly bill for this car, then you have every right to get mad at your sister. if this is the case, you need to sit down and have a "nice" talk with her, telling her that the car will be reported stolen and she will have some explaining to do with the local authorities. i think i remember you saying in your last thread like this that she does have her own car, so maybe take her car for a drive and "test its limits".
there are 1 of 2 things that is happening to your car....
1. she met up with a boy at starbucks and she let him "take it for a spin"
2. she just gave you that story as an excuse to go on her own joyride.
either way, you can bet you would be brought to tears if you saw how your car is being treated with her in the seat. (driver and passenger seats)
everyone here is giving you a lotta crap for "letting this happen again"...having a little sister (i call her monster for good reason) i can actually understand that it may not be a matter of you "manning up". if she wants to drive the car that bad, she will find a way, which she did.
to those of you bashing the OP, unless you have a sister that is a total bitch like mine, you shouldn't be bagging on the OP. at least my sister can't drive a manual transmission.....and i hope she doesn't drive stick IYKWIM*
*if you know what i mean