For the person who came here looking for "things to say when breaking up"...here's a hint embrace that you are the black hat in this scenario. You are. Curl up with that for a moment. Give it a cup of tea. Be one with it. You are going to hurt this other person. No matter what. There is no good way to do this. You do not get complain. You do not get to say "Do you think this doesn't hurt me?" Your pain is your choice. You can't make the choice and then complain to the person who has no choice in the suffering. Nope.

This does not mean you can just do anything you want and to tell with it since it is going to be bad-there are gradations-you have to choose between bad and worse.

Worse would involve saying "It's not you, it's me" "We can still be friends" or "I care about you."
If any of those are true, you won't need to say it. If you same them, well, on top of being a heartless twit you're also an unimaginative moron who doesn't even care enough to come up with a genuine and unique approach to this person you until recently cared about.

If the person lashes out at you, YOU DO NOT RETALIATE. You have hurt this person deeply. You can at least have the decency to take a pot shot or two from them. Don't heap petty insult on top of heartbreak.

In the comments field Lux added that now is not the time to bring up the other person's personality flaws, issues, or to blame he/she for this EVEN IF IT IS TRUE. Don't worry, blaming oneself for a break up is a given. You don't have to help.

Also courtesy of Lux avoid the L word. She said don't say "I don't love you," but I would say just leave it out altogether.

I would say try and make it as easy for the other person as possible-ie don't do it a few minutes before the person has to go before her/his bosses and give the most important presentation of his/her career-have some sensitivity in selecting the time and place of the break up. This may be uncomfortable for you-tough.

The idea of "embracing the bad" to make things easier for the other person-ie "oh if I'm a COMPLETE prick it will make it easier for the other person to accept my rejection"-doesn't work. It will simply mean the person, on top of being rejected, will question his/her judgement that he/she had no idea what a prick you were. It may inhibit he/she from getting involved with someone. Do not compound an already bad situation.

Oh and dropping a box of stuff in his/her lap at the end of this conversation-not cool. If there is a stuff exchange, you might consider giving the person some time. If he/she seems to want to do it right away, you should have things ready in NICE CONDITION for return. Sensitivity is the key here. Depending on the other person, he/she might need time to adjust and then deal with the stuff issue.

Those are my thoughts on the topic, anyone else?