I always have to look up how to apply sticky bit/suid/sgid, so I am bookmarking it here for future reference.

tl;dr:

Command Effect
chmod u+s a file with this set always executes as the user who owns the file
chmod g+s a file with this set allows the file to be executed as the group that owns the file; a directory with this set causes files created under it to have their group ownership set to the directory owner
chmod o+t file can only be deleted by its owner