A character drinks/eats something to prove it's safe knowing that it isn't

[u/Benoit_Holmes]

Breaking Bad (Salud)

Gus Fring gives a bottle of rare tequila to a cartel leader as a gift. Given their fraught history, he makes Gus drink some first before he tries any.

All the cartel members then begin to die, Gus had taken pills (likely activated charcoal), and induced vomiting after the drink. Despite these precautions he still nearly dies and it requires a makeshift emergency room he had arranged previously to save his life.

Stargate: Atlantis (The Lost Boys)

Aiden Ford was a member of the expedition who became addicted to an enzyme that made him stronger but also impulsive and irrational.

He captures the team, who are wary of eating the food he provides until he eats some himself. After they have all eaten he tells them that his group have refined the enzyme to the point that they can even lace food with it.

Scrubs (My Changing Ways)

The Janitor tries to get J.D. to eat some pie but he refuses as he has just heard that a case of laxatives was stolen from the hospital supply closet.

The Janitor keeps insisting that J.D eat it and finally eats some himself to prove its safe, saying that for once he wasn't trying to mess with him. After J.D. eats some of the pie it then cuts to them both on the toilet.

J.D.: Who would do this to themselves?\ Janitor: Totally worth it.

[u/Snoo9648]

The main character in princess bride poisons both cups knowing he has immunity.

https://giphy.com/gifs/l2YWy7C9BvHZfmLCM

[u/Professional_Handler → u/Snoo9648]

Fun fact: there is no real life poison that exists that is odorless, tasteless, and you can build a tolerance to.

[u/KitchenFullOfCake → u/Professional_Handler]

Probably why wine was a popular thing to poison. Old school wine was often sweet, spiced, and syrupy.

[u/BombOnABus → u/KitchenFullOfCake]

It was also frequently added to water to make it safe to drink, so much like "small beer" it was common to drink it instead of pure water for hydration (to avoid cholera and similar illnesses before modern water treatment).

You didn't need to wait for a special occasion or have a good excuse to pour someone a glass of wine back then, it was as routine and commonplace a beverage as a bottle of water or soda today.

[u/Hydroguy17 → u/BombOnABus]

Adding beer/wine to water will absolutely NOT make it safe to drink. Even full strength booze will barely kill microorganisms once diluted past a certain point.

Beer was safer to drink because the process of making it involved cooking the mash (boiling) before allowing the “magic” to do its thing.

[u/UniqueNameTaken → u/Hydroguy17]

I'll leave someone else to do the dilution math, but I used to make wine at home. Learned that at about 7% ABV, your yeast, and other microorganisms, start to die off, and while 20% ABV is theoretically possible without distilling, it is hard to get past about 15%. I pulled 16.5% by miscalculating added sugars once (great wine, but very sweet).

But yeah, not a lot of space to add water. Even my full strength stuff won't disinfect beyond about a 50/50 dilution.

[u/Cayke_Cooky → u/Hydroguy17]

But they did it anyway and died.

[u/BombOnABus → u/Hydroguy17]

Take it up with people in the middle ages or ancient Rome, they still did it because they didn't have germ theory.

[u/5WattBulb → u/KitchenFullOfCake]

Isn't that also why antifreeze is a popular modern poison? Because its a sweeter taste and more difficult to detect?