Geek Stink Breath song meaning

"I liked speed because I wanted some rocket fuel. I wanted to think that's the difference between us and the grunge scene: we wanted to go faster." - Armstrong.

The author is not making a secret out of what the song is about - "I'm blowing off steam with methamphetamine". Geek Stink Breath is about drug abuse and its consequences. "Geek" is one of the slang words for methamphetamine, and combined with the fact that using meth makes your mouth dry and gives you a bad breath, it gives the unhealthy combination of geek stink breath.
The narrator is giving the listeners a detailed description of what is happening to him as he walks "the path of self-destruction" - his teeth are rotting out, his heart is not working properly, his blood is "turning sour". The line "I'm picking scabs off my face" could be about hallucinating, since it's been described by meth users that the intoxication gives you hallucinations of scabs on your face, along with an unbearable desire to tear them all off. So, the narrator admits that drugs are messing him up, and yet he states that it's all that he's got and he's not planning to change anything.

Even though the author claims that the song doesn't express any particular opinion about the use of meth ("It's not really for it, and it's not really against it. It just describes a state of mind, and the destructiveness it had on me personally." - Armstrong), it's obvious that Geek Stink Breath describes the negative part of drug abuse. And to add to the grossness of the lyrics, the video to the song contains graphic scenes of tooth extraction. It is, in fact, so disgusting that it wasn't even played on MTV in daytime ("MTV won't play it during the day anymore. It's a little graphic" - Armstrong). So, maybe there is no actual "meth is bad" message in this song, but the vivid description of what the use of it will lead to makes it pretty clear that this song is not about the fun of doing drugs, but about the aftermath of the destructive addiction.