It's really Jealous Guy. But I'm more of a stupid guy than a jealous guy, so that's how I sing it when I sing along...or when I sing it in the shower.
I love the whistling Lennon does here. (I like whistling along too.) He and Paul McCartney always seemed to have loved whistling. One song on which McCartney warbles is The End of the End, his song about his own death on the 2007 release, Memory Almost Full.
Interestingly, we usually associate whistling with happiness. But this song is more on the sad side. And, I suppose Macca's whistling on a tune about his own demise would be considered ironic. It sounds good no matter the effect for which he was aiming.
Jealous Guy appeared on the 1971 release, Imagine.