Because that's what you are.
3 seconds sound clip from the Boyz n the Hood movie soundboard.
You can hear this line at 01:08:41 in the Blu-ray version of the movie.
Quote context
[...]
- You tell me this, nigga. How you know God's a he? He could be a she. You don't know that.
- For one thing, you don't know what the fuck I be motherfucking knowing.
- Why every time you talk about a female you gotta say bitch or ho or hootchie?
- Because that's what you are.
[...]