Nah, I’m just pumped, I bought some shit from a thrift shop
He’s explaining the overconfidence/ arrogance exhibited in the previous line is because he just got a lot of stuff from the thrift shop. He’s expressing that the first line is how he feels after copping all the fly shit from the thrift shop but he wouldn’t, really, walk into a club and deliver such a “dickish” line (pun intended).
“Nah” indicates that he’s kidding about the first line. To strengthen the couplet, he says, “I’m just pumped.” I hope he’s not referring to this kind of “pumped”:
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