And that’s flat!
Definition 1 of 1
Pro Tip 1/3Strong Assertion
Shows the speaker's strong commitment to a decision or opinion. 
I won't lend him money again, and that's flat!
Pro Tip 2/3Ends Discussion
Indicates the speaker does not want to continue discussing the issue. 
This is my final offer, and that's flat!
Pro Tip 3/3Casual Tone
Often used in informal situations rather than formal or professional settings. 
You're grounded for the weekend, and that's flat!