At night, New York, eat a slice too hot
Use my tongue to tear the skin hanging from the roof of my mouth

from Nas (Ft. Large Professor) – Loco-Motive Lyrics on Rap Genius

New York is famous for its pizza that is hot and cheesy.

Also, this could be a reference to his song, Represent from Illmatic:

This nigga raps with a razor, keep it under my tongue.

Were Nas to have a razor under his tongue, it could be used to “tear the skin hanging from the top of his mouth”. As in to say he raps in a sharp/intelligent manner.

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