What does "that" refer to here?
Sheldon is re-enacting a conversation between his parents in which his mother says, "I told you if you didn't stop drinking I would leave you". Sheldon's father's response is "I guess that makes you a liar because I'm drunk". "That" here is in reference to her statement that she would leave him. Clearly, she hasn't left so her statement is proof that she is a liar.
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