"Talk broken english and drug sellin" is a line that KRS-One uses in his seminal 1987 song My Philosophy. The line comes at the end of a couplet addressed to then popular rappers Run-DMC:
some mc's be talkin' and talkin'
tryin' to show how black people are walkin
but I don't walk this way to portray
or reinforce stereotypes of today
like all my brothas eat chicken and watermelon
talk broken english and drug sellin'
At the time, KRS-One was portraying himself as the "teacher" as opposed to the self appointed "kings" of Run-DMC. The couplet gives an example of two different Run-DMC songs, "Yakity Tak" and the Aerosmith crossover "Walk This Way". At the end of this train of thought, he argues that not all people "talk broken English and drug sellin" (as far as I know, Run-DMC has never portrayed black people as drug dealers).
The humor of the line, of course, comes from the fact that it itself is in broken english, although the form of dropping the superfluous verb is not one I think is typical in black speech.
The line is further emphasized by the fact that KRS-One doesn't emphasize it. He could have changed his voice to an "uneducated voice" or a "street voice". However, he says the entire line in a clear annunciation, without exaggerating it, and proceeds to the next line.
It is thousands of clever little tricks throughout his raps that have made KRS-One one of the best MC's ever.