I'm old school, I still abide by my version of the old GT5P open room philosophy that was discussed to great length on the Sony forums.
1. Contact between consenting adults is ok, just keep it to yourselves and don't assume everyone races that way.
2. Race rules encouraging contact is ok and when appropriate, encouraged.
3. All other forms of contact light/heavy or otherwise is unacceptable and should be avoided.
We all make mistakes. Especially in the limited environment of a video game. Contact will happen, we all do it.
When contact happens:
1. If you wreck the person, pull over at a safe and appropriate time and give the spot back.
2. If you don't wreck the person but take a position in a questionable way, give the spot back at the next appropriate time.
Where to stop/give back spots:
1. Way off the racing line on straights
2. Pit road
3. use run off areas that do not affect the flow of the race.
4. Do NOT stop/slow down on the racing line, while in the middle of a pack, or in turns.
5. DO get out of peoples way first.
When these options are not available
1. Apologize through available communication resources
2. Correct the situation in the next race. (not revenge)
If a person makes a mistake and does not make up for it, its best to call them out. It's possible the person may not be aware that they did something wrong. We all use different driving views and controllers and simply cannot feel or see everything that happens. If need be resolve it in private chat.
Pay Back or "taking someone out" is unacceptable. If your at that point park/leave the race, take a break and remember its a game and we are all here to have fun.
Race clean, race hard and let the duck win.
and in the words of Forrest Gump: "That’s all I got to say about that"