The "adult" way to dump someone is to do it in person.
I mean, getting dumped is obviously always going to suck, but making an effort to dump someone face-to-face shows a certain level of respect toward your soon-to-be ex.
That is, unless you're one of these nine people who were broken up with — in person — in some of the most savage of ways:
She dumped him the day after taking his virginity.
He dumped her while they were still naked in bed.
— Maggie*, 25
She got dumped on New Year's Day.
She smiled as she told him she never loved him.
She woke him up in the middle of the night to dump him.
She dumped him after seeing him naked.
She went out of her way to show him she chose someone else.
She ran over to the guy she was cheating with.
She dumped him with a cookie.
Honestly, the cookie one doesn't sound that bad to me...