I tar and feather featherweights until my 'fetti straight

from Royce Da 5'9" (Ft. Travis Barker) – Legendary Lyrics on Rap Genius

Meaning

“Tar and feather” is a sort of vigilante justice where someone who is presumed guilty has tar thrown on them and feathers thrown on the hot tar to embarrass the guilty.

A featherweight is a weight class in boxing/mixed martial arts known for its small fighters.

“Fetti” = http://www.urbandictionary.com/define.php?term=fetti

So Royce is saying he’s embarrassing the soft, under-belly of popular rap all the while making sure he makes his money.

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