See a man about a dog

This expression dates from the mid-19th century and is a euphemism for whatever a man has in mind to do without being explicit. In America it is sometimes used in the form of ‘see a man about a horse’. Apart from when one is genuinely going to see a man about purchasing a dog or horse, there are generally three recurring contexts in which it is used: excusing oneself to go to the toilet, going off to a tavern or bar to have a drink, going off to see a mistress or lover.