You are so wrong. its not even aeuphemism. its something you say when you want to get out of a situation.
Mr Ed
Illicit gambling based on inside information (can refer to dog as well as horse), a bit hush hush, used to leave present company with a knowing wink and (vitally) no questions asked.
Gallant800
You say this when you have to take a pee and you’re with a group of people. It’s a line of excusing yourself. As in, “Excuse me for a minute, I need to go talk to a man about a horse.”
Henry
Can mean needing to use the lavatory. A polite way to say your not interested in a conversation. A term for shady business.
euphemism: 1. the substitution of a mild, indirect, or vague expression for one thought to be offensive, harsh, or blunt. 2. the expression so substituted: "To pass away" is a euphemism for "to die."