98% of my racing experience has been in roundy-round racing, but I suppose the attitude (or etiquette) is the same on any race track. If you put your car on the track, you are putting it at risk. If it gets crashed, whether it's your fault or not, tough cookies! You knew the risk when you rolled onto the track.

If you crash into someone, you might want to say you're sorry, but it sort of depends on the other car owner's demeanor. If he is really upset because you did something really stupid that caused the mishap, you might want to give him time to calm down or you could get your face dislocated...