see a man about a horse
verb
°(slang idiomatic euphemism) A message signaling one needs to urinate (used mainly of men).
"Wait for me here. I'll only be a couple of minutes. I've just got to see a man about a horse."
°(slang idiomatic euphemism) A message signaling one needs to go missing for a short while, for any reason, without giving a real explanation.