I only mentioned that to one T that I saw about 5 years ago. She became alert and looked for a safety contract to sign, couldn't find one so I made a verbal contract with her. I had no intention of doing anything..I was just explaining thoughts.
My former pdoc wouldn't let me leave the office and called my mom to pick me up (even though I was 26-27 at that time) otherwise she was going to call 911.
This is very, very t/psych/pdoc specific when it comes to how they will react. I do encourage you to be honest with them though. They are only there to help you. And them them that your thoughts are just that, thoughts (unless they are deeper, of course).
Good luck