pony

The leg muscles - more specifically the quads. Only used when the legs are large/strong enough to merit their own mention. Hiking up one's pants or unisuit is another way of displaying ones ponies - this is referred to as a "pony show."
Used mainly by Long Island rowers or anyone similarly severely disattached from reality.

"Yo my ponies are yuge."

"We got an audience today, time to give em the pony show."