My answer: there isn't one! Like, officially... stop faulting people for not being honest or direct enough, stop criticizing or talking about how facebook breakups or text message breakups or a post-it on the door just isn't "right". Stop acting like there are supposed to be rules!
Because every time I tried to break up with a guy, I got raked through the coals over it. I tried honestly telling a guy that we needed some space, he blew up at me for being so "sudden" about this, told all his friends I'd been dishonest because I'd been secretly thinking that it wouldn't work out but held it in for so long (as if I had the answers, saw the future, just didn't tell him?). Then he'd call me at random times asking if we'd get back together, and if I said I didn't know he'd ask why I was stringing him along, and if I said "no" he'd accuse me of once again, having all the answers, how long have I known that it wouldn't work out?
So the next guy I tried just fading away, filling up my schedule, not answering his phone calls, and friends said I was leading him on too. And finally he chased me down and did the "we need to have a talk why are you being a shithead why don't you just BREAK UP WITH ME if that's what you want?!" I'd been hoping that I could get him to break up with me, so I wouldn't have another crazy angry ex-boyfriend talking shit on me everywhere. It only sort of worked. Well, to be honest, it worked better than the upfront conversation strategy... shitty as people made me feel about it.
By the time I met Marc I was so sick of crazy ex-boyfriends and bad breakups that I didn't want any boyfriend, period. I knew that no matter how normal a guy is, you have no idea how he'll react when you break up with him!
So I told Marc that. Early in the relationship, in fact, I laid it all out and said, "I just want you to know that if I decide I don't want to be with you, THAT'S MY RIGHT! I am not obligated to find out the perfect way to say it, I am not an evil person because you are not right for me, I am not saying anything about YOU by ending a relationship. You are not allowed to freak out!" And oddly enough, he totally agreed, in fact he'd had psycho ex-girlfriends and knew exactly what I was talking about. No hard feelings, we agreed. We had a breakup plan in place, we were ready to go before we even got serious. Both of us knew it was going to be the best breakup ever.
Except then we got married. So, crap, there ya go.
But at least I have this advice out there for the world... do not be mad at your ex-boyfriends or girlfriends. Move on! Maybe they cheated on you because they didn't know how to break up, and if they put your health at risk you should be mad, but aside from that I can't think of a situation where you should feel entitled to a form of breakup. They happen.