99% of things in Prop 65 are fine in moderation. And the 1% that isn't (I would love to be warned of that myself) - well, it's lost among everything else.
To be truly informative, binary cancer warnings should be rare -- they should appear near a threshold where reasonable people are likely to be swayed by them (but not certain to be swayed by them -- at that point we're probably labeling too few things.)
But enough about binary labels, though. They should have to put figures on them: "Scientists believe that the cancer risk of this cup of coffee is statistically expected to decrease your lifespan by 5 minutes, plus or minus a day, with 95% confidence."
Really no idea what would be in it that is worth being worried about.
I could only think maybe there is something used to assemble it with lead in it?