Everyone is calling everyone a rat so much, it means nothing now.

I can be running through a building and turn a corner, face first into another guy. Short gun exchange, and he dies....and he starts cursing me out for being a rat.

I can be somewhere in an area looting things without being quiet. Breaching, running....and someone comes up and pushes on me. Then I down them, and they start cursing me out for being a rat.

8/10 times someone is bitching and moaning in game, it's calling someone a rat.
The word has lost all meaning, other than "someone who killed me"