Here, Groucho performs it on The Dick Cavett Show. He refers to the song being by his good friend Mr. Ruby. That would be Harry Ruby, who did the music and generally wrote with Bert Kalmar. The team is in the Songwriters Hall of Fame. Among their great-many other songs, they wrote "Who's Sorry Now?," "I Wanna Be Loved By You (and Nobody Else)," the Oscar-nominated, "A Kiss to Build a Dream On," "Three Little Words," (their biggest hit and title of the movie made about his and Kalmar's partnership) and "Nevertheless" (which I posted a video of here sung by the Mills Brothers).
But it's the lunatic comic songs they wrote for the Marx Bros. which is why they might even be better known for today -- and how he and Groucho, of course, became friends -- like, "Hello, I Must Be Going" from Animal Crackers, "Hail, Hail, Fredonia" from Duck Soup, and "I'm Against It" from Horsefeathers. (Also performed in Horsefeathers was an earlier song they had written, "Everyone Says I Love You," which though a popular standard song was used to great comedic effect, as all the brothers separately sing it -- even, in a surprising way, Harpo. Woody Allen used it as the title song in his 1996 film musical.)
And with all that aside, this is the song of the day.