Jenna Moran's blog posts on learning Chinese are excellent, and who knows how long the Eos-sama website will be up after all the shenanigans. So, here's an archive.
Eos’ Jesse Covner clarifies that bù (不) does not mean “don’t.” So you can’t use it to stop that bird! That bird can laser you all it likes and you can’t say bù.
A Book of Divine Letters: Second Aside