2 year old stout is bitter as shit!

[Captain Scotch]

My Uncle brewed a stout a couple years ago and the keg has turned into a 5 gallon pot of bitter black coffee!!! I had a couple pints a few months ago and it was delicious (albeit after a few glasses of IPA), but how could it turn so acrid after just a few months? He doesn't have any temp control and he severely overcarbonates every keg... What happened?! Is there any way to salvage it?!

[Captain Scotch]

Was it just the hops going away and the black patent malt taking over?

[BDawg]

You can blend it with another beer that isn't as bitter.
You can boil up a bit of lactose and add that to help balance the bitterness.
Lower the carbonation also will help to reduce the perceived bitterness a little bit.
(Think of the difference between plain water and highly carbonated plain water).

[peas_and_corn]

Was it just the hops going away and the black patent malt taking over?

That would be my argument too. Dark roasted malts add a coffee-like bitterness to beer, which matches up with the description of the beer in the OP. So yeah, probably the way to go is blend with another beer, preferably something light and flavourless.

[bigBbrews]

I agree with bdawg I had a stout also get a bit to bitter,I accidentally overcarbed it and once I realized I just dropped the co2 pressure and purged off the excess and let it sit a few days and wasn't to bad.