No. If left out in the sun or heat, it does get “skunky” which effects the taste. It will be still safe to drink.
IOW, identical to Amaretto bought yesterday.
What will get skunky? That’s a beer thing, due to the way hops break down in the presence of light. Vodka, gin, tequila, etc., ain’t gonna skunk.
Heh. Exactly what I was thinking. 
(But, no, I get it. It will concentrate over time as it evaporates so it will be a bit sweeter and thicker.)
I have a bottle of 12yr old single malt that went what I can only call “skunky”. :(:(
Not vodka, no.
I think 5-10 year open bottles are really common. Back in the day, it was a thing to have a well stocked bar in your home. I knew people who had basement bars with 20 opened bottles of various liquor in stock so they could make any exotic drink you wanted. I’m betting some of the bottles that the host didn’t care for had been open for a decade or more.
Me too. I can’t remember the brand but it was an excellent highland single malt. I had about a quarter of a bottle stashed away that I forgot about until I moved. The bottle was stored in a nice wooden presentation case. The scotch had gone cloudy. It didn’t even look right sitting in the bottle. I tried to open the bottle and failed. It had a cork stopper and the stopper broke leaving cork in the neck of the bottle. I useda corkscrew and mostly got it out, but the remaining cork disintegrated and fell into the scotch. I strained some of the scotch off and tried it. It was awful. I threw it out.
Surely thats what teenagers are for?
My experience with even quite nice bottles of wine - I’m very partial to stickies - has been that its better to drink now rather than run the risk of leaving some and forgetting to polish them off until the mega-spring cleaning of the booze cupboard brings them to light a decade later.
Some (spirit-based) liqueuers improve with age - I have bottles of sloe gin that I make most years - when they’re about a year old, the drink is purple-pink, slightly astringent and fresh-fruity; when they’re five years old, they will have turned a sort of tawny brown colour and have flavour notes that are like prunes and raisins - it’s as though the fruit continues to ripen after being infused into the liqueuer.
I compared a freshly-made batch with a ‘vintage’ bottle in this video: Random Stuff - Sore Throats, Sloe Gin and Spicy Noodles - YouTube
I have no palate, so I don’t worry about the liquor being old. After the third drink, it all tastes the same anyway.
Regards,
Shodan
PS - John 2:10
How about a jug of Everclear, or some other nearly-pure ethanol? Can anything go wrong with that?
If any air can get to it, it will slowly lose alcohol content, being replaced by water, mostly.
Liver function ?
Now you tell me. Where were you 12 years ago? I was sick for days!
Are you kidding? After my grandmother died, I took home the contents of her liquor cabinet – most of the stuff was at LEAST 15 years old, and unopened. And damn, she had some GOOD stuff. Pretty potent, too. 
(A Creme de Menthe that was to die for – I think that was about 20 years old or so. Some apple peach brandy, that was good too, then some blackberry brandy. The Amaretto wasn’t too bad either.)
We had a bottle of some chocolate cream liqueur go bad last year. We’d opened it about 4 years before and drank a third. It was disgustingly mouldy inside.
Just last weekend we also had a bottle of some lower alcohol berry liqueur that was bad. The bottle was about 50% consumed and it was very oxidized. No cream in this one, just alcohol and sugar and probably artificial flavours. We’d bought it a few years ago during a martini craze and my out of the blue my wife decided she wanted another one saturday night. One sniff and down the drain, back to a Bahama mama!