I bought a plain T at Walmart for $3.00, got some interfacing, and some plaid fabric.
I then cut out two pieces, the "knot" of the tie and the "tail" of the tie (sorry no pics because I am a slacker ).
I then sewed on the tie with a zig zag stitch all around the edges. After that I ironed on the interfacing under the tie inside the shirt.
Here is the end result:
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