I know this is a joke, but if anyone’s curious: Prop65 says you have to tell people if your product contains chemicals from a list of carcinogenic substances. The list is kept up-to-date by California. Prop65 has no punishment for over-reporting though - you can slap on a warning “just for fun” if you want.

Unless California has aspartame on its list, prop65 says nothing about this.

Saw a California shirt once that was a prop65 warning: "This shirt has been determined by the state of California..."

No aspartame, but aspirin's on there. https://oehha.ca.gov/proposition-65/proposition-65-list