Listen, I don't know if you're playing dumb or legitimately so, but do not joke about such a thing with someone who mentions they're depressed.
I'm not someone that would act on that (at least I don't think), but plenty would. If someone were to kill themselves because you or someone else made a comment like that? That's negligence at it's absolute worst, so I don't care how seriously you take someone when they talk about depression or suicide, do not make remarks like that. If you can't say anything else, don't say anything period.
Hm, not seeing anything negligent. Others aren't my responsibility to begin with, but wasn't encouragement to do so just a consult on the implementation they choose.
Have to get our furnace replaced so today is going to be talking to sales people a lot. Wonderful, but 16 years is probably near the EOL of the unit, so can't be avoided (well, it can, we'd just need to do without heat)