You, etc. should be so lucky
Definition 1 of 1
Pro Tip 1/3Sarcasm Alert
The phrase often has a sarcastic tone, suggesting that the desire is a dream far from reality. 
Win the lottery? You should be so lucky!
Pro Tip 2/3Not Literal
It's not a genuine wish for someone's good fortune but rather a way to express doubt. 
You should be so lucky to date a celebrity!
Pro Tip 3/3Conversation Tone
The phrase is informal and commonly used in casual conversation or friendly banter. 
You think you'll beat me in chess? You should be so lucky!