Learn English – Idiom for making fun of an unpleasant situation

If you mock someone’s misery, you rub salt into their wounds, described in the Oxford Learner's Dicionary as:

to make a difficult experience even more difficult for somebody

This Dictionary of Idioms gives a fuller definition and example:

Rub salt into the wound/(someone’s) wounds to make (someone’s) sorrow, shame, regret etc worse, often deliberately: I was very disappointed at having to miss the concert, and my friends kept rubbing salt into the wound by telling me how good it was.

And two examples from the media, where rubbing salt into the wound specifically means mocking someone’s misfortune:

City fans mock Manchester rivals: [Manchester] United let a 3-1 lead slip to lose 5-3 at Leicester yesterday, before City took on Chelsea at the Etihad [stadium]. And cheeky Citizens fans took the opportunity to rub salt into their rivals' wounds with an aerial banner. “United we fall ― in cinemas soon," read the message flown over the Eithad.

Hilarious Comeback Joke Takes Off On Reddit After English Mockery: Last week, rugby fans around the world cruelly wallowed in England’s early World Cup exit. Several jokes were posted online and it seemed as if England’s closest neighbours were most keen to rub salt in English wounds.

I always understood this to mean "this is no fun and a waste of time" and that the "game of soldiers" or "lark" we thought it would be - has turned into something far less fun. I.e. "this is a rubbish game of soldiers" "this is no fun if it's supposed to be a lark" The "Sod this/blow this/ ___ this" is meaning "who the hell thought this would be a good game of soldiers.