Definition of that's it
1 —used to say that something is finished or completed Okay, that's it. You can go now.
2 —used to say that something is all that is needed or wanted I came here just to visit the museum and that's it.
3 —used to say that something is correct "I can't remember his name." "I think it was Brian Johnson." "Yes, that's it."
4 —used in an angry or annoyed way to say that one will not accept any more of something That's it! No more horseplay in the house.!
What did you just call me?! A Quiz