Swing

Swing is the official Java GUI toolkit. It's also a steaming pile of shit.

To verify that the steaming pile is indeed composed purely of shit, follow this procedure:

Start a Java Swing application of your choice.
Poke around in the GUI for a minute or two.
Note the drawing bugs, the inconsistent and unattractive spacing, the odd focus glitches and the horrible font rendering.
Now, consider that this GUI toolkit has been worked on by a large team of engineers continuously for over ten (10) years. It's not a beta release.
Thus we can see that it's fundamentally crap. Crap == shit. QED.