That yomper big as Larry Johnson,

from Earl Sweatshirt (Ft. Casey Veggies & Vince Staples) – Hive Lyrics on Rap Genius

Meaning

His gun or “yomper” is as big as Larry Johnson, a former NFL player with the Chiefs who came at you at 6'1 and 235 lbs.
Vince’s gun is huge, be afraid, be very afraid.

He may also have meant former NBA player Larry Johnson, being that he was known for his sheer size and strength as opposed to NFL Larry Johnson who is big in his own right but not like grandmama (his nickname)

#wrongdudetofuckwit

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