@Ceki ....Skye promised that the "Report Function" will be activated when they launch the new version of MDL soon!
Meanwhile, you can try POLITELY telling the author of the spoiler to mark it as such .... That has worked for me in the past! ..... Most people don't realize they are spoiling plot....
BUT some will stubbornly not respond!!! .... these spoilers should be reported directly to Admin or staff via PM, so they may remove comment ....
There are several Spoiler comments out there, I am waiting for the function to start working, and then report them.