From a minor (not *proficient* in PHP) point of view, ignoring a thread on its own is not possible.

The only way I know to make sure you ignore a thread is to:

1. Respond in any thread you might have interest.
2. Subscribe to all threads you respond to.
3. Remove from the subscription any thread you do not like.
4. Once a day, hit the 'new posts' so you see what else you might want to be part of.
5. Read emails for threads instead of actually on the forum.

Rinse, repeat.

If anyone else comes up with 'ignore thread', I would be interested to hear it, as would several PHP-coders I know!