Just don’t do it.
Specially when you’re riding in the front seat of a car, and sticking your hand and phone (or tablet, I’ve seen it personally!) out, blocking my view of the right side mirror. In the interest of public safety, please sit at the back of the car. These should be mutually exclusive: take selfies, or sit in the front seat, don’t do both, you’ll get us killed. I won’t even say please anymore.
I had a few near misses because my passenger insisted on sitting at the front, while taking selfies and blocking the right side mirror–and still kept on taking selfies shortly after my protests.