In BrE, you could use bagsy not, but it doesn't sound right here.
I was taking swimming lessons in the pool with two other guys, and the instructor asks us to do sth in whatever order that we like (ie who goes first, who second and who last). So the other two guys didn't want to go first, so they both said a slang which i had never heard of and is driving me crazy. it sounded sth like "shadi not", meaning "not me"! So I had to go first. I assume it's something like "bunny up" to decide who goes first, but obviously in reverse order!
Anyway, I can't find the exact slang. So do you may be know what it is? It's killing me!
Please be aware that I'm neither a native English speaker nor a teacher.
Maybe they said, "shotgun, not me." 'Shotgun' is a slang, meaning if someone in a group is the first person to say "shotgun", that person will make the first decisions for themselves on their own behalf. This is done in a playful manner.
I belive the entomology of the phrase 'shotgun ' comes from the era of Stagecoaches, the driver would sit on one seat, the guard armed with this type of weapon would sit next to him. The idea of a person claiming the passenger seat of a car, by saying 'shotgun' came about, and eventually it morphed into people saying it to claim the right to go next in any situation. It is common in AmE, but not BrE.
not a teacher
It sounded sth like "shadi not".
I think that "shotgun" is indeed the answer here, although the person probably said "Shotty not ...".
See this Urban dictionary link and the example "Shotty not taking out the trash".
I have heard "shotty" used to mean a shotgun, but only in direct reference to the firearm.