Sources close to the embattled rapper tell TMZ ... Tekashi is well aware of the hate he's been receiving either on camera, in interviews or on social media from his peers, but he doesn't give a crap about any of it -- 'cause he thinks those folks are foolhardy haters.

In fact, we're told Tekashi has strong words for those people -- which is a LONG list at this point, BTW -- and it goes something like this ... just wait and see.

According to our sources, Tekashi believes him testifying against his old crew will be forgotten almost instantly as soon as he's released from prison -- and he also thinks he'll be more popular than ever with the masses ... which, of course, means $$$$ in his pocket.

We're told he thinks that anyone in the rap game who's spoken ill of him since this whole legal ordeal began are not only envious, but threatened by him ... afraid that he'll pass 'em up and leave 'em in the dust when he gets out and starts making hits again.

Those are strong words for a whole lot of folks, including Cardi B, 50 Cent, Meek Mill, 21 Savage, Snoop Dogg, Jim Jones and others whom we didn't even speak to directly. There's more artists we talked to that are pissed, like The Game, Irv Gotti, Skinnyfromthe9 and even Rap-A-Lot Records honcho J. Prince. They've all condemned him.

6ix9ine isn't paying much mind to any of it though, apparently. Seems like he's going down the ignorance-is-bliss road and sticking to it, all without witness protection to boot.