A very stupid and easy way to die would be to pee into a bottle of bleach. For some reason, it doesn't seem that unbelievable, that someone who really needs to pee could stumble upon an almost empty bottle of bleach and just go for it.
First of all, the mixture would release deadly fumes which would then definitely kill you. Additionally the chemical reaction could cause the mixture to boil and splash that nice toxic mixture onto you.
So make sure you never have a bottle of bleach lying around whenever you host a party or there'll be deadly consequences.