Just back out how you normally would and be on your way.
What is normal though? For me - I have an extended bed truck with an industrial topper that blocks most of my rear vision. I can only use my door mirrors.
I think it’s harder to back in simply because you have the constraints of needing to be within the lines. That means people will do it slower and will probably still have to straighten the car out. When you back out there aren’t any lines you need to be in.
You have line and vehicle constraints when backing in, with a small chance of encountering a pedestrian. Yes. It is slower than going in forward. And more difficult.
When you back out, you don't have line constraints, but you now have moving vehicle constraints - plus, moving pedestrian constraints are much much higher. This is what frightens me the most. I don't mind paying to fix someone's car that I damage.
I don't know how to fix a child that I have accidentally ran over.
Therefore, I am afraid that I will always be one of those people that annoy others by slowly backing in. I understand why I may piss people off, but I am not going to change my method.
Also when you back out, you are forced to wait for traffic to be clear to do so. However, plenty of people try to back in with traffic behind them, expecting the people behind them to be psychic enough to stop far enough back or go around.
In a parking lot, with vehicles adjacent to me, I have a very very very hard time judging when traffic is clear. I almost need to back out part way to even tell the condition of traffic that I may encounter.
As far as backing in with traffic behind them ... I understand the frustration. Thus, I always try and park far away from the dense section of the parking lot. This is not always possible tho. If I find that someone has not stopped behind me, I will keep looking for another spot.
But, I would still prefer that idiot who is holding me up - to just hold me up - rather than run me (or others) over later.