To claim possession of something for when you return, such as a seat. Short hand for the phrase "quack quack I get my seat back"
Counter arguments include:
1. Move your feet, lose your seat
2. Cluck, cluck, I don't give a fuck!
Abby gets up from the couch and says, "Quack!"
Abby has 'quacked' her seat, thus no one else can take it.