When I pull up out front you see the Benz on dubs
When I roll twenty deep it's 20 knives in the club

from 50 Cent – In Da Club Lyrics on Rap Genius

Meaning

Now that 50 is rich he’s going to flaunt it by hitting up clubs in his luxurious Benz. A ‘'dub’‘ is a 20 inch rim and is used to put emphasis on style; anything less is just not gonna cut it!

‘'Rolling twenty deep’‘ is both a continuation of the previous line (rolling with 20 inch rims) and also means that he’s rolling with 20 of his homies. When he got his gang with him they’re bound to start a few fights in the club; only proper etiquette for a G to prove their worth.

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