Peter
Oh Dear I do that all the time and sadly I consider it a good skill to have , namely you have a limited field of vision in the game , unless you stretch your field of view , the number of times I have stood very near to someone and they obviously dont know I'm there, so part of the skill is knowing who is where.
Also if I backshot someone and miss they normally turn round and kill me 🙂
The other thing is how can there be etiquette in an FPS ? Its always been a free for all 🙂
When I played dom with a proper translocator not a grapple , there was a platform where you could drop your translocator then fall off the platform backwards wait a few seconds , then rematerialise on the platform killing any enemy that was on there , Unless they had spotted and killed your translocator , I did it so often (admittedly more effective on pubs than clan matches ) that I got muscle memory to do it , properly impolite though it was