A somewhat
antiquated expression that means you're dressing in a flashy,
ostentatious style. You're out to impress people with your slick clothes.
"Bill, putting on the dog tonight, huh? What lovely
lady are your taking out?"
The expression, which comes to use from the 19th century, has its origin in the custom of rich people owning
lapdogs, like
Maltese dogs. Lapdogs were popular in Ancient Greece and
China. During
Queen Victoria's reign, she was given some lapdogs as gifts and they became an instant
rage in
England.
So basically, no one going out the door and dressed for society was complete without a
tiara, a cape, and a highly pampered
pooch on the end of a
leash.