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Phrase(s): that’s why!
a tag on the end of a statement that is an answer to a question beginning with why. (Shows a little impatience.) • Sue: Why do you always put your right shoe on first? Bob: Because, when I get ready to put on my shoes, I always pick up the right one first, that’s why! • Mary: Why do you eat that awful peppermint candy? Tom: Because I like it, that’s why!
McGrawhill's American Idioms And Phrasal Verbs