A long time ago (we're talking post-disco-era-zoic times here, folks) I use to hang out with a circle of friends that communicated with a strange language. They were obsessed with the Russian/English mix used in "A Clockwork Orange". No, we were not anything close to the Trench-Coat Mafia.
Among the gang was AOC (Airhead of the CENTURY) who lived in his car. Another was Jerry, who always spoke in 3rd-person format. He would never say "I" but would always refer to himself as "Jeddy", which was his adopted nickname at the Chinese restaurant he used to work at. He had the entire English language condensed down to SIX WORDS:
JEDDY: Jerry; me, myself and/or I
GO SIDE: Any form of movement, such as "change the channel", "get out of the way", "duck!" or "turn left; turn right". Driving this guy home was a nightmare. These two words were always used together.
NO PING: Anything bad, such as an 80's TV sitcom or a Yanni concert. "PING" by itself was the opposite... anything good.
Example: "Jeddy go side, no ping!"
Translation: "I am going away now, this movie is real boring."
M: SLOW! Jerry did not invent this, but someone else from that same circle. When that someone-else a was kid, his father would yell at him, "You're as slow as molassis in January!" His brother then started calling him "Mr. Molassis", which truncated down to "Mr. M." and finally abbreviated itself to just plain "M".
So, when is the proper time to use the word "M"?
1. You are at a grocery store, waiting in the Express Lane behind a woman who has at least 50 items, lots of coupons and a check book. If you are with a friend, you look at him, he looks at you, and you both simultaneously flick three fingers down (designating the letter 'M') and hum out loud, "M!"
2. Traffic jam - you are stuck behind a guy driving half the speed limit while clacking his jaw away on the cell-phone. In this case, the proper use of the "M" hand signal is to rest the fingers on the dashboard.