If you’re using X11, you can use xkill: https://en.m.wikipedia.org/wiki/Xkill

You can bind it to a key in gnome/kde (not sure how they handle custom keybinds. Otherwise add a call to xbindkeys to your .bashrc or equivalent). It kills any window you want, responsive or not.

As for the terminal, I don’t think you can send SIGKILL, but ctrl + \ will result in a core dump if you’re using bash.