Today is my 29th birthday. Both my parents, independently, sent me roughly the same birthday message, containing the following line, which is traditionally sung by my grandfather as a coda to "Happy birthday to you...":

And she lives down in our alley
without a shirt,
a dirty purple shirt....

I have no idea as to the meaning or origin of these lines, and I'm afraid to ask. "She Lives Down in Our Alley" appears to be an old barbershop quartet song, but I've Googled "dirty purple shirt" and come up empty. The connection to "Happy Birthday" remains a mystery.