Under certain circumstances, do you ever flash your lights to communicate to other drivers when you're driving?

If I’m on a two lane, fast highway, and there is a car at the intersection waiting to pull out, and if I have the impression they haven’t seen me, I’ll flash my lights. More than once they will have been “rolling,” meaning they let up on the brake (I hate that,) and they suddenly come to a full stop when I flash.

I also flash my lights as I start to pass a semi. (When I was a beginning driver I stupidly passed a semi on the right. I was in a little Vega and the semi started moving into my lane. My dad was behind me, watching in horror! But I started flashing my lights and laying on the horn and he saw me in time.)

On a two lane, when a semi passes me, I flash my lights when they’ve cleared my car and can safely pull back over.