This word is commonly used by die-heart wingmen, cheaters, people still stuck in-the-closet and drunks.
Also commonly used to describe an ugly, fat, or or just plain unattractive people who you would never consider being with.
An attractive person, is hardly ever a duck.
I got so drunk last night that I woke up sleeping next to a "duck".
My girlfriend and I had to leave the party early last night because I've seen one of my ducks there.