1) Refers to XXX-rated live stage female performers ("ponies") that will use only one stallion as a sex partner for all performances.
2) When said, it is a jab at Joe Biden not knowing the correct saying of "one TRICK pony" when he snapped at a reporter that was tenaciously asking questions about his son Hunter's alleged wrong doings with regard to international financial transactions.
"I don't know what she's going to do when they put that stallion out to stud!" LOL
"C'mon man! You're a one horse pony on that question, I'll give you that!"
President-elect Joe Biden called Fox News correspondent Peter Doocy a "one-horse pony" after he asked a question about reporting over the federal investigation into his son Hunter Biden's laptop.
Yet another equine themed Biden gaffe. He probably meant "One-trick pony".
"Yes, yes, yes. God love you, man. You're a one-horse pony,"-- Joe Biden 12/22/2020