Why dont you just sit down and talk to this person? Calling him/her a loon isnt likely to solve anything. As for the examples you have given of tampering - stocks often get misplaced accidently, experiments dont always work as expected, and perhaps someone just knocked over your tubes in the waterbath - Ive had water leak into tubes once as I didnt seal them properly and they got knocked over :( Maybe these thinks didnt just happen by accident, but you should talk with this person and make it clear you would report any further tampering as professional misconduct....