A friend of mine started a thread, and this was the message…
Share away, folks! 
My take? The thin line exists between “You’re doing something that I consider bad/negative and I insist that you stop it” and “You’re doing something that I consider bad/negative and I’m going to force you to stop it”. It’s not necessarily the sentiments expressed… it’s how you express them.
I think we all know people for whom this is not a thin line at all – who have the sort of human dignity that prevents their being walked on or acting impolitely. You could argue that acting like a jerk is a form of being stepped on – you have allowed someone to provoke you into losing your cool, thereby confirming that you didn’t really have enoungh of it.
One of the best responses to provoking behavior is a pointed silence.
It’s fine to assert your rights, but it’ll go down better if you are polite and/or diplomatic.