Well, Ely, that's kind of akin to my accidentally singing "How's about keepin' something up for me" instead of the actual lyric to Hank Williams's "Hey, Good Lookin'"   
It was at a memory care unit of a nursing home (maybe they thought I should be a resident?), and I'm not sure anyone noticed but me. (Let's hope not.)

Now, just last week I did a popular Hanukkah song and I THOUGHT I had caught myself before mixing up a lyric that goes:
"O Hanukkah, o hanukkah, come light the menorah.
Let's have a party, we'll all dance the hora."

But when I played back my video of the gig, sure enough, in one of the three times I sang those lines, it came out:
"O Hanukkah, o hanukkah, come dance the menorah!"

Oy!