This is a brilliant thread and I can relate to most everything that's been said. I know the S3 is a "family" car but there is a limit to the anguish I can take. In consequence, I have mandated my wife, daughter and grandchildren as follows:
1. scratchy bags, brollies and other paraphernalia to go to in the boot, but only I can place them so as not to mark the boot.
2. only I can close the boot using the internal notches to do so.
3. wipe feet before entering car.
4. only use door handles to close door from outside; otherwise, do not touch bodywork.
5. ensure that fingers/hands are free from make-up, hair lacquer, nail varnish and MacDonalds before entering car.
6. don't sit on walls, park benches etc and then expect to be allowed back into car.
7. remove seatbelts soundlessly; any hint of buckle contacting B pillar will be regarded as a heinous offence.
8. great grand daughter's buggy must have clean wheels before being allowed in boot.
9. anything else not covered above.
If anyone would like to add to this list, please feel free to do so in the interests of vehicle preservation.