Originating from the italian word Ambrosini.
Generally used when someone backs out of something at the last minute. Sometimes used when complaining about previous arrangements made and then had plans changed.
To commit a "jambro" you must make some sort of complaint and then retract from participation.
Act of: leaving a man behind. To be in a "jam", "bro"
Related to: Janston and Sandy Vagina
1: Committing a Jambro:
"Hey, you are gonna play catcher now, I'm going to play second base."
"Hey man! NO WAY!!! I didn't spend $7 at the batting cages for nothing, I'm out of here man, play without me!"
"Oh man, don't pull a jambro".
2: Using Jambro:
"Come on man, we need one more player on our team! We are one short!"
"Naw man, I don't like to play football, I am going to go play WoW"
"Aw, don't pull a Jambro"
Also see Sandy Vagina