Old stagecoaches had two people sitting on top of the carriage. One was the driver, the other carried a shotgun to defend against Indians and bandits. Riding beside the driver is riding shotgun.
Riding Shotgun - 2012 V is rated/received certificates of: Australia:MA
There isn't an idiom that means riding a lamb - people make idioms for things that are commonly seen or done, and people don't really ride lambs much.
"Riding shotgun" means sitting in the front seat of a car. Before a car journey, if you are quick, you can call shotgun and you get to sit in the front seat.
Riding Shotgun - 2013 was released on: USA: 4 October 2013 (Woodstock Film Festival)
if a lot is riding on someone, they have a lot of pressure or a burden. I think the expression is a gambling term. One might say that a lot is riding on a big bet. Perhaps, it came from betting on horses where a lot is literally riding on a horse if one has placed a big bet on him.
Greensburg Kentucky
The cast of Riding Shotgun with Jack McConaha - 2005 includes: Jack McConaha as himself
Riding shotgun?
Lawman - 1958 Riding Shotgun 1-29 was released on: USA: 19 April 1959
It is not an idiom, it means your nose is itching.
It's not really an idiom. It means "what are you thinking about."
RFP is not an idiom. It's an abbreviation.