This was a lovely story, featured on the BBC this morning. A Russian man, before signing a contract with his bank, altered the small print, signed it, and sent it back to them. They signed it, not noticing that they were then obliged to provide interest-free loans, no management charges, and would pay a substantial penalty if they wished to get out of the contract...

Fabulous idea.

I've done nothing as cunning as that, but often when I call some institution and get an automated voice saying "This call may be recorded...", I say "Thank you!", and click the record button...

That'll show 'em.