Having been on the receiving end of being rear-ended by a truck since I had to stop suddenly (due to the truck tailgating me on the motorway just before the terrace tunnel) I've learned to be quite conscious with who is behind me. The truck who rear-ended me wrote off my car along with 3 cars in front of me so you could imagine the type of impact it was. Still though, walked away from it without any injuries however the driver of the truck was a complete idiot.
Now, if I have space to go I'd give them a way to pass but I have been known to be a little evil and let them pass me right before a speed camera if there was no reason for them to be tailgating me (karma).