I have some never opened alcoholic bottles under the kitchen sink and has been there for years. The are basically whiskey, vodka and bacardi. I always thought that alcoholic drink never go bad and even the taste doesn't spoil and can be kept for years but my other question about wine got me thinking if that is not the case. So can we keep alcoholic beverages indefinitely without even spoiling their taste? 
Short Answer:  Yes. In general, unopened containers of alcohol have an indefinite shelf-life.  For example, there are 500+ year old barrels of wine which are likely still drinkable (i.e. not only safe to drink, but pleasant).  Alcohol itself is a preservative, and will prevent nasty organisms from growing.  As such, I would not have any safety concerns about old bottles of liquor (especially if they are still sealed, but even if they are not---I have a bottle of whisky that I have been sipping on for about 20 years).  However, there are things which can change over time. Beer When beer is exposed to ultraviolet light, it can become skunked.  This is why beer is generally kept in brown or green bottles, as these are better at blocking UV light than clear glass.  It is also worth noting that one of the defining features of beer is its effervescence—those tiny bubbles of CO2 are part of what makes drinking beer pleasant.  Once opened, the CO2 comes out of solution pretty quickly, leading to flat beer. Mold can also grow on the surface of beer, or in a container which has been in contact with beer (e.g. homebrew equipment which is not properly sterilized).  Properly bottled beer will not grow mold as long as it is unopened.  Once a bottle is opened, it can be exposed to mold.  However, mold is typically pretty obvious, and the beer will no longer be pleasant to drink long before it gets moldy. Thus opened containers of beer will likely remain perfectly safe to drink for a longer period of time than they are pleasant to drink.  Unopened containers should remain safe virtually indefinitely. Wine, Cider, and Sake Wine continues to change and evolve after it is bottled.  There are some wines which improve with age, and others which are meant to be drunk "young" (e.g. [1] and [2]).  Wine also reacts with oxygen, and changes significantly once it has been opened, which will changes its flavor and character over a short period of time (e.g. you'll notice significant changes after only a few days—eventually, you'll have vinegar). Sake and cider are similar.  Unopened bottles will generally change very little over time, and opened bottles will react with oxygen. Finally, as with beer, sparkling varieties of wine (such as champagne) go flat fairly quickly after they are opened. Again, just for emphasis, wine which as been sitting in a bottle for a long time is generally safe to drink, but it may not be pleasant. "Hard" Liquor Hard liquors, like whisky, rum, tequila, and vodka will basically never go bad, and will experience very little change once they are bottled.  For something like vodka, which has very little flavor, even opened bottles will change very little over time. For more complicated liquors, such as whisky or rum, which are aged in (and take on the character of) barrels, the complex molecules which carry flavor and aroma can react with oxygen.  However (in my experience), these changes are very subtle, and have very little effect on the overall experience. In short, something with a higher alcohol content is going to be both safe and pleasant to drink for a very long time, either opened or unopened. Dairy There are some drinks which contain dairy, e.g. Bailey's Irish Cream or (appropriately for this season) eggnog.  These types of drinks are often lower ABV and may have some risk of spoiling.  However, it will generally be pretty obvious that the drink has gone off, as the milk will curdle. Again, I would imagine that sealed bottles will last basically forever, and I would have no problem drinking from an old bottle if there are no signs of spoilage.  But if you do see or smell something off, throw it away. It should be obvious. 