For one of my presentations I searched for some time for a way to make my own server process get into a spinning and hung state. I found the best example in this SQL, which spins on 188.8.131.52 and can be run by any user, including non-privileged. When I had a friend run it as a non-privileged user on a windows server, it made the server almost unusable, and necessitated stoping the Oracle service to get things back to normal.
SQL> select 1 from dual where regexp_like(' ','^*[ ]*a');
The statement will not return, and you may not be able to ^C out of it. The server process/thread will consume all idle CPU and the time will be spent in uninstrumented code (STATUS=WAITED SHORT TIME and SECONDS_IN_WAIT > 1).
Don't run this on any system that you can be fired for bringing down! You have been warned.