Oi oi, I'll rugby-kick the shit out your groin, boy

from El-P – The Full Retard Lyrics on Rap Genius

Meaning

A subtle nod to punk rock here. Oi! is a U.K. punk subgenre that is traditionally working-class and often flirted with far-right politics. Quoth Wikipedia:

[The genre took] the name from the garbled “Oi!” that Stinky Turner of Cockney Rejects used to introduce the band’s songs. The word is an old Cockney expression, meaning hey or hello.

The “kick” part is referring to rugby and the kicks they use.

This chant can be heard at rugby matches.

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