Dash: Typing NUL (Ctrl-Shift-@) will sometimes open a lot of windows (local DoS)
This one was pretty special at the time. I wished I'd had video!
The Dash currently displays/interprets all characters typed in it. In particularly Ctrl-j (enter), Ctrl-c, Ctrl-v, are all displayed by their raw Unicode values rather than the actions that are most usually associated with these functions.
On once occasion (I haven't managed to reproduce it so far) I managed to send Dash/Launcher off into an unresponsive state where the machine continued to open a huge number of windows in the background at a rate of ~4/second each titled sladen. Eventually further windows stating "Unresponsive ..." started popping up. Eventually I rebooted. This was witnessed by johnlea.
I have not been able to repeat this, so it's possible that the particular sequence of control key codes (Unicode value) I typed possibly lead to a lucky buffer overflow or similar.