Should old acquaintance be forgot, and days of old lame signs. Or something like that. Most can hum or whistle the tune. Maybe even play it on a kazoo. That's about all I can say about it, other than no one knows the words.
Singers can vouch for that.
You're the professional, so you're supposed to bring this song in. The first line is the only one the general public knows. For auld lang syne, me dear, for auld lang syne. We'll take a cup of kindness now, for auld lang syne. We two hae run about the braes, and pou'd the gowans fine.