Potion of booze
A non-blessed potion of booze will make you confused for 3d8 turns. ("Ooph! This tastes like liquid fire!") It will also provide some nutrition and abuse your wisdom. (10 nutrition if cursed, 20 if uncursed, 30 if blessed, regardless of dilution.) If the potion is cursed, it will make you pass out for up to 15 turns. If the potion is not diluted, it will also heal 1hp. A blessed potion of booze will not cause confusion.
If the potion was diluted, it will taste like "watered down liquid fire", and it will taste like "dandelion wine" if hallucinating.
Potions of booze are sometimes used in conjunction with the scroll of gold detection on the elemental planes to detect magical portals, or in conjunction with the scroll of enchant armor to prepare for the fire traps in Gehennom, especially by Monks and Wizards, but note that this is only useful with uncursed potions, since the desired effect is confusion.
Dipping an amethyst into a potion of booze will turn the potion into a potion of fruit juice. This is a reference to amethysts' name coming from Greek ἀμέθυστος ("not drunk"). See the article on amethysts for more details.
junk → water → sickness → fruit juice → booze → blessed booze.
In dNethack, booze is actually useful as a source of nutrition. Drinking it gives 130 points of nutrition if uncursed, 140 if blessed, and 120 if cursed. However, drinking a cursed potion will cause you to vomit for 15+5d4 turns afterwards, possibly losing some of that nutrition. Booze will also heal you for HP equal to your level when quaffed, no matter the BUC of the potion.
Drinking booze now implements a "drunkenness" counter, which tracks the number of potions you've quaffed (BUC doesn't matter for the sake of the counter). If you are stunned, or 1⁄5 of the time if you are confused, and you've drunken more than three potions of booze total, you have a
1 / (number of potions drunk/3 + 1)
chance of not moving where you want to go. Again, while confused this only triggers with a 1⁄5 chance, so your chance of moving unsuccessfully while confused is (formula) / 5 and equal to the formula while stunned. This applies to any source of confusion and stunning, not just from other booze, and doesn't affect your chances of getting confused or stunned in the first place.