I've always kind of seen this song as being kind of an answer song/takeoff to "I Saw Mommy Kissing Santa Claus"; it's from the point of view of the father rather than the kid, and turns out "santa" is just his friend trying to hit on his wife. The line about "humming cheating songs" kind of reminds me of an old joke about a prudish woman complaining about hearing neighborhood kids humming dirty songs when they walk by her house, The humor of course being that you can't really know a song's dirty unless you're already familiar with the words. So maybe it's a hint that he wasn't always that faithful himself.
I've always kind of seen this song as being kind of an answer song/takeoff to "I Saw Mommy Kissing Santa Claus"; it's from the point of view of the father rather than the kid, and turns out "santa" is just his friend trying to hit on his wife. The line about "humming cheating songs" kind of reminds me of an old joke about a prudish woman complaining about hearing neighborhood kids humming dirty songs when they walk by her house, The humor of course being that you can't really know a song's dirty unless you're already familiar with the words. So maybe it's a hint that he wasn't always that faithful himself.