Oh, better give me your hat, Jack 'fore I snap back
Or else I'll decapitate your head and fit it in a backpack

from M'Balls (Ft. ScopeY) – RG Battle Round 1 Lyrics on Rap Genius

Meaning

Some may be aware of the fact that M'Balls is actually a notorious hat stealer and will jack your hat if he pleases. He was most recently seen in the Michigan area so be careful.

Wordplay with the different synonyms of hat:

Hat — snapback — de-cap-itate — fit it/fitted

If you are not willing to give him your hat he will take it from you thus de-cap-itating you.

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