My words are like a dagger with a jagged edge
Em is here making fun of the idea that his words are so dangerous (the theme of the song is that his lyrics are treated like deadly weapons by people who accuse him of encouraging violence or homophobia); the over-the-top description may be about highlighting the absurdity.
Incidentally, a dagger with a jagged edge would be more painful to be stuck with than one with a smooth blade, in the same way that you’ll be more ripped by sharp teeth than by smooth teeth. Not only are Em’s raps aggressive (i.e. dagger-ous(?)), but they are sharp/well-executed (i.e. the jagged edge).
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