When someone needs to change lanes at the last second, do you let them in?
For me it depends on the situation. If I see someone cutting in and out of traffic, nothing makes me happier than to squeeze them out.
I also live near a intersection that has 2 right turn lanes. I stay in the outer one because I have to turn left at the next light, about a block away. Too often people in the inner lane want to turn left also and will practically change lanes directly into me. So everytime I go through there, I make sure to stay next to or ahead of the cars in the inner lane so they can't cut in front of me. Am I just being obnoxious or just taking care of myself? I think the latter of course.