comparing someones intelligence to the speed of a horse finishing a race. the slow horse would natrually finish last, therefore the person who is the 'slow horse' is not very bright.
1. someone of minimal intelligence or who does not understand simple concepts
2. someone who is illeterate
3. often used to call someone stupid when they dont understand something, commonly a simple joke
4. a dumbass
can add the word "dusty" in front to mean a person who is both foul or dirty as well as unintelligent
BOBBY: OMG, I was trying to talk to Amanda this morning, and she just had the most stupid look on her face like she was confused by the most simple sentance!
MICHELLE: She is such a slow horse, it's like talking to an infant.
AMY: Wait, who are we talking about again?
BOBBY (to AMY): Wow, you slow horse.