That's the name of a horse I used to own, ma'am.
4 seconds sound clip from the Fear and Loathing in Las Vegas movie soundboard.
You can hear this line at 01:43:32 in the Blu-ray version of the movie.
Quote context
[...]
- She looked like a burnt-out caricature of Jane Russell. She was definitely in charge here.
- He did it very casually, but I knew that our peace was about to be shattered.
- Don't give me that bullshit. I know what that means, you fat goddamn pimp bastard!
- That's the name of a horse I used to own, ma'am.
- The question mark was emphasized.
- Anybody that knows anything knows that.
[...]