Lyric discussion by the_music_nazi 

Cover art for Heart Shaped Tumor lyrics by De/Vision

It's about suicide.

"Put an end to yourself."

It's really about the sadness of being in a relationship with the wrong person, or with someone who doesn't feel the same way about you as you do about them. Once you realize that, life may not be worth living. So maybe you'll decide to put an end to yourself.