If it avoids diffusing into air to the degree that you can scoop it up and pour it, I’d imagine that it’d pour out of one’s lungs the same way.
But if you just want to get most of it out of your lungs — like, you’ve been breathing it and don’t want to asphyxiate — I imagine that exhaling all the air you can and inhaling air and doing that a few times would probably do a pretty good job, the way the Mythbusters video above did with the helium.
I assume so. Here’s a video of someone floating a boat (apparently in air) in it, and then sinking it by pouring cups of sulfur hexafluoride over it:
https://www.youtube.com/watch?v=ee2NaYRnRGo
If it avoids diffusing into air to the degree that you can scoop it up and pour it, I’d imagine that it’d pour out of one’s lungs the same way.
But if you just want to get most of it out of your lungs — like, you’ve been breathing it and don’t want to asphyxiate — I imagine that exhaling all the air you can and inhaling air and doing that a few times would probably do a pretty good job, the way the Mythbusters video above did with the helium.