If there is traffic behind me, I drive normally so as not to annoy or trigger road rage. There is little cost in the Niro in "normal" takeoffs a few times daily. I doubt you could notice it on your tank mpg.
I know that it can be really tickoff to someone who is behind you if you are trying to start and get going while trying to keep the HEV in EV mode. In my case it felt like that jerk behind me was mad that i didn't leave rubber on the road like some takeoff sports car modes. But I don't see anyone getting to violently mad when behind an 18 wheeler and they don't seem to start very fast, nor public transit busses, so I tend to point the finger at the person behind who is honking and getting mad as being the cause of any road rage. Lefts face it, we all get stuck behind someone who we feel is a bit of a dumbass at some point in our driving life. But also most of us don't flip out because of it.
2018 Niro EX - Ocean Blue
GTA - Canada.