A monocle walks into a bar...

 A monocle walks into a bar. After a few drinks he starts to feel pretty good (and a little uncoordinated). He reaches for a cigarette, but the bartender stops him. "Sorry, buddy, but due to city ordinances we don't allow smoking in here. You'll have to step outside to smoke."
So the monocle hops off the bar stool and grabs his cigarettes to head outside. Meanwhile a second monocle emerges from the bathroom. They bump into each other as they cross paths and fall to the floor, hopelessly entangled. They try to get free but the more they struggle, the more tangled they become.
The bartender looks down on this travesty and shakes his head. "Hey you two!" he shouts. "Stop making spectacles of yourselves!"

This is a moderately long joke, but the punchline is pretty good, so I doubt that it would be considered a shaggy-dog story. The humor in this joke is centered around a pun. To make a spectacle of ones self is defined as "to do something in front of other people that is very embarrassing", and falling on the floor and getting hopelessly entangled with another bar patron would certainly be something that could be considered embarrassing.

On the other hand - a monocle is a single lenses that is used to enable the wearer to see better, and a pair of spectacles is a pair of lenses used in the same manner. So, if two monocles were attached to each other they could be considered to be a pair of spectacles.

This isn't that bad a joke at all.