Another way of phrasing this is:
I am using a stereotype when I say the Chinese can't drive for shit.
A stereotype is:
A set idea that people have about what someone or something is like, especially an idea that is wrong (Cambridge Dictionary)
They have changed the noun stereotype into a verb form. This is called gerunding (See what I did there?)
As 1006a points out, the entire phrase is:
Ain’t nobody telling me I’m stereotyping when I say that the Chinese can’t drive for shit. They just can’t, and that’s that.
This is saying that people may say they are being stereotypical in saying the Chinese can’t drive for shit, (as it is arguable that while some may not be able to, some are likely to be proficient drivers) but they are arguing that they are not being stereotypical, and asserting it is a fact.
This is ironic since despite by denying being stereotypical, they are admitting to their stereotype.