Sometimes a process w/ a window hangs. Imagine a recursive shell command with a typo.
Get the offending process's pid via click, and kill in one command:
kill -9 $(xprop _NET_WM_PID | cut -d' ' -f3)Here -9 tells kill to send SIGKILL, which can't be caught/ignored by the target.
xprop reports X server window properties. The _NET_WM_PID property contains the pid, and we cut the 3rd field separated by a space to get just the pid.
Finally, the $(...) bashism substitutes the retrieved pid into the kill command, resulting in kill -9 "pid of what you clicked"