In Nodwick, we have "Skullwhomper Ale". The effects are rarely shown in the comic itself, but its consumption almost invariably leads to some sort of Noodle Incident. The destruction of the local tavern it is served in is a frequent component to these, and when a local Elven/Dwarven war takes over the town, the invaders end up classifying the ale as an incendiary weapon. Skullwhomper Ale was initially brewed by a dragon who did intend to use it as an incendiary weapon. When it found out that people were stealing its concoction for drinking, it was so embarrassed that it gave Nodwick the recipe and completely gave up on its plan.
In the webcomic Freefall, John Jones Monroevian Moonshine: Fine sipping whiskey and high explosive. According to the ingredients list on the bottle, it contains "muskrat squeezings, nitroglycerin, and other additives both natural and unnatural." This is, of course, a Shout Out to the Kickapoo Joy Juice in Li'l Abner (made from ground up dead skunks and old shoes among other things).
Florence: 'If you drink this, you will die.' Pretty clear warning label.
Helix: Uhm, that's the statement of quality. The warnings are listed further down.
In Girl Genius, Theo's idea of a good home-brewed liquor can be expected to be at least 200 proof, and have other... interesting ingredients. "Hey, he's breathing again!" One cup of Lingonberry Snap will apparently give you hallucinations. "Ah. I'd wondered why they were playing the music backwards." Note that 200 proof is pure alcohol. Also note that under normal circumstances, opening a container of pure alcohol outside of laboratory conditions will cause it to be diluted by the moisture in the air. Maybe part of Theo's talent as a Spark makes him a Mad Moonshiner who can make impossible drinks?
One strip of Planescape Survival Guide has a drink made from the exploded remains of a Balor demon being handled with tongs, and the hilarious aftereffects of the drink itself.
Stickman And Cube has Una Muerte Con Mucho Dolor, which comes with several hours of warnings and disclaimers and must be served in a diamond glass.
Death: Pardon the stereotype, but you're a dwarf. I know you've got a better drink for us. Dwarf: Well... there is one drink... but the last time Thor had some he went blind for a fortnight.
Something Positive recently introduced an accidental one, with Davan taking a swig from a flask... not realizing Monette had dumped Everclear in it... and Fred had dumped moonshine in it... and PeeJee had dumped absinthe in it. He instantly started hallucinating imaginary characters from Girls With Slingshots, the comic whose characters' wedding he was attending at the time.
Another time the group asks for a liquor store's "finest whiskey" and gets it. bottle glows and singing angels can be heard, and just one sip was enough to allow alcoholic Faye to see quantum mechanics. It also glows.
Faye: Everything's... blueshifted... a myriad of quantum states... all of them deliciously intoxicated... Hannelore:(reading label) "Warning: Consumption of this bourbon whiskey may cause you to get religion, get naked, or get arrested." Dora: It doesn't say anything about relativistic time dilation. Maybe we should call the hospital. Or a physicist.
An unidentified alcohol in a later strip is just as ominous.
In SSDD a CORE bar serves "99% proof cider", it's also the only thing that can get the Super Soldiers who make up a significant proportion of their clientele drunk.
Tessa: I thought the "Do not drink" label was just a marketing ploy!
Lee: Yeah, legally they need to sell this stuff as paint thinner.
Brog ale in The Gods Of Arr Kelaan, the fermentation process involves sulfuric acid and something like nitroglycerin and even Brogs can only drink one a day. Ronson (god of alcohol) gets a little numb for a few seconds if he drinks enough of it fast enough.
