The lyrics to the song "Stein um Stein", which describe the process of building someone into a wall. While they're still alive. See for yourself here.
"Mein Teil" also deserves a mention. Partly because it's about the real-life case of Armin Meiwes — indeed, the lyrics are preceded by Meiwes' ad for a young man to be "slaughtered and then consumed" — and partly because in the middle eight, there's a noise in the background that sounds like dying screams. As if the fact it's an eerie metal song about cannibalism sung in a foreign language creepily weren't enough, read the story behind the song in excruciating detail. Yes, he really did that to his you-know-what (hence the title, 'Mein Teil', which means 'my part' in German). And if you're still not convinced as to how frightening the song is, watch the music video.Sweet dreams...
The stage show isn't any less disturbing. Till dresses up as an Evil Chef, with what looks like fresh blood running down his shoulders, smeared across his mouth, and spattered along his clothes. He shimmers, like he's covered in some mixture of sweat and grease, spends much of the song sharpening a knife with a steel and routinely grins and licks his lips at the crowd.
Rammstein generally have either lyrics about sex or murder or both. There are two songs about plane crashes, one about an insane man shagging his decaying dead wife, "Wo Bist du?" (Where are you?) about a man searching for someone in order to knife them. "Ich Tu Dir Weh", so bad that the German government has put it and the album on which it appears, Liebe ist für alle da, on the Index. This means it cannot be sold to minors. (to be fair, the artwork shows them killing and eating women.) And "Haifisch" (Shark) is based on the chorus of "Die Moritat von Mackier Messer" (The Ballad of Mack the Knife).
The masks in the "Du Hast" music video are nothing short of Uncanny Valley.
The cover art of Mutter.
The weird kitchen-object face masks on the Sehnsucht cover.
"Donaukinder", based off Baia Mare cyanide spill, is also scary — both the lyrics and the music itself (with its use of extremely heavy guitars and Ethereal Choir), as typical for Rammstein.
The piano version of "Mein Herz Brennt". The song is creepy enough as it is, but among a lone piano is just disturbing. Till's appearance in the video doesn't help matters either.
Towards the end of "Das Alte Leid", a song about the complete pointlessness of the whole cycle of birth-life-death because it only gives rise to yet more suffering, as the band keeps repeating the chorus, you can hear deep in the mix the sound of a baby crying. It goes on. And on.
"Engel". It's a song about how, if you're good, you'll rise to Heaven and become an angel... and then you get to spend the rest of eternity cold and alone, with no way out. The stage version involves a flaming cage.