Can’t be bad
Definition 1 of 1
Pro Tip 1/3Positive Spin
Implies something is better than just acceptable, often with a hint of surprise. 
You got a free upgrade? That can't be bad!
Pro Tip 2/3Subtle Sarcasm
Sometimes used sarcastically to imply that something is actually quite good. 
A whole beach to ourselves? That can't be bad, can it?
Pro Tip 3/3Emphasizing Luck
Used when acknowledging a fortunate situation or outcome. 
She won the lottery on her first try—that can't be bad.