What's the worst way to break up with someone?

Headbutting them

"I'm sleeping with your mom."

Via Morse code.

on their birthday and they caught you in bed with someone else

At their relative's funeral . . . Ouch.

Stop talking to them all together.

In a text message

In Klingon.

There was an episode on how I met your mother where Ted broke up with a girl on her birthday. After the second time dating her.

Give a speech on national tv describing him (or her) as deplorable

introduce the new bf/gf to your instant ex.

Probably in a Pogonophile or Kali thread.