Don't care whether it's slash or not (or established/non-established if slash).

I'd like Sherlock to be all 'well i don't know how to gift so i bought a dog is that okay' (one reason could be that Redbeard was a gift for Sherlock and Mycroft so he learned from there)

John's confused at first, very shocked, but then is very happy with his gift

+one thousand internets for John's reaction being so fuckin' happy he hugs Sherlock and won't stop thanking him and alternates between adoring the dog or Sherlock first
+a thousand and one if it's Christmas you choose and John had bought him something much lamer than a dog and is a little embarrassed
+a billion if the dog has a lil bow ≧◡≦