Somebody won’t thank you for something
Definition 1 of 1
Pro Tip 1/3Negative Outcome
Use this phrase when someone's actions will likely result in someone else's displeasure or annoyance. 
If you eat the last cookie, your sister won't thank you for it.
Pro Tip 2/3Sarcasm Implied
The phrase may carry a sarcastic tone, emphasizing the negative impact of an action. 
Spilling coffee on the reports? The team certainly won't thank you for that.
Pro Tip 3/3Subtle Warning
It is often used as a soft warning to consider the consequences before acting. 
Canceling the meeting last minute — your clients won't thank you for it.