I've been told that basicly what he is talking about is that the chick thinks that her sh*t doesn't stink (suggesting that it smells good ie. like roses) but if she were to pay more attention, that it actually smells like everyone elses.
Going deeping into that, that entire thing is a metaphor for someone thinking that they are all that, but really they aren't. I'm probably not explaining it very well, but... yeah, that about it.
Unless you actually meant to bash the entire song, in which case I don't really care one way or the other.
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Humm, guess I should put something witty here, huh?