I’ve been flagging during time a couple of posts, the other days snitching on one of my own posts, and the system was not giving the First Flag badge.
In fact it had offered that flag only one time and besides that I doubt that I am the only snitch on the block… 
Or, who knows… 
It is only you.
Then it considers that’s not snitching if it doesn’t give the prize… 
No idea about the badge, will see if I have one as the only other flag activity was during early functionality testing.
The
First Flagbadge will not be awarded, unless a post has been flagged asoff topic,spamorinappropriate
From discourse support.