I can count on one hand the number of times I have actually had a "fight" while being in a relationsihp - I am generally non confrontational and I am particularly mindful of saying something I know will hurt the other person.
With that being said, I once had a girlfriend who had a vicious mean streak, and she was routinely rude to not only me, but my friends as well. First couple of times I let it slide, but I reached a point where I had enough. I sat her down and said "You grossly overestimate how much I value you or our relationship - I am just as happy without you as I am with you, so feel free to leave at any time".
I have never seen someone go from hostile and confrontational to a sobbing mess so quickly. It stung so much more because she knew that I meant every word of it - I didn't say it out of anger (like calling someone a bitch etc), it was simply the cold truth. I guess in her head she thought I was head over heels for her (and I suppose I am guilty of cultivating that perception), but in reality, I am the exact same in a relationship irrespective of how I actually feel. When I have broken up with people in the past, in tends to blindside them, because they assume I'm really into them.
In any event, the relationship didn't last. That is probably the worst thing I have ever said to someone.... that, and "I love you", when I never really meant it.
