Formal:
* Underperform: This implies that something didn't meet expectations but doesn't necessarily mean it was a complete failure.
* Not achieve desired results: This is a more neutral and objective way to say that something didn't work out.
* Experiencing difficulties: This implies that there are obstacles or challenges that are preventing success.
* Missed opportunity: This suggests that something didn't go as planned, but focuses on the potential that was lost.
Informal:
* Bomb: This is a slang term that suggests something was a complete disaster.
* Flop: This is another slang term that implies something was unsuccessful.
* Go belly up: This is a more colorful idiom that means to fail completely.
* Not quite make the cut: This suggests that something was close to being successful but didn't quite meet the requirements.
* Didn't pan out: This implies that things didn't work out as planned.
* Hit a snag: This suggests that there was an unexpected problem or obstacle.
* Fall short: This is a more neutral way to say that something didn't meet expectations.
The best euphemism to use will depend on the specific situation and the tone you want to convey.