How do I fix an app that's stuck in application switcher?
In Terminal.app, find the process ID for Dock with the ps aux | grep Dock command and kill it with the kill -9 PID command. An example:

$ ps aux | grep Dock
username              290   0.0  0.4  2730344  34500   ??  S    Fri08PM   0:22.48 /System/Library/CoreServices/Dock.app/Contents/MacOS/Dock
username             3633   0.0  0.0  2432784    612 s000  S+    8:06PM   0:00.00 grep Dock
$ kill -9 290