Also known as Suicide is Painless, lyrics by Robert Altman's 14-year-old (at the time) son. Through an interesting circumstance related to publishing, Mike Altman got a royalty from every rerun of MASH, despite the fact that the lyrics aren't used on the show. He had a super-bitchin' house up on Camano Island in Washington. I dated a girl who went to high school with his son, whom I also later worked with on a show, as well as Robert Altman's other son, Bobby, cinematographer responsible for "the Player pull:" Both Bobby and Jade were f'n awesome. I was sitting down to lunch once and Bobby said "I'm really boning you in all these shots." (Bobby likes to use lots of cameras, which makes it really hard to get a boom in, and the show was... challenging). "It's all good, Bobby, it's part of the gig." "No, but you're totally handling it. My dad would have loved working with you." Probably the highest praise I'll ever receive for sound, and I'm A-OK with that. I was walking on air for weeks.
Apparently Robert decided it had to be called suicide is painless and that it needed to be "the stupidest song ever written". He struggled with it himself for a while and then had Mike write it, who apparently managed to throw it together in about five minutes. Here's an interview that details the subject. Though I suppose you personally have probably heard the story first hand!