Then I pray you don't drive!
You sort of are excusing the trucker.
You write as if you haven't been involved in many and I hope that continues for you.
I have and in those situations, I do often throw my hand up (actually, I usually sweep it out left to right first, and then up in the air, blessing the incompetent with a sign of the cross, because they need divine protection, as do all they meet). It's not remonstration or looking for confrontation, but more trying to wake the following drivers up into not slavishly following the offender and making another close pass. It's actually slightly better to do it before the vehicle has passed, while in the offenders' blind/low spot if possible, because then the offender doesn't usually see it and so a confrontation is less likely. I'm stable enough to take one hand off the bars and still have control (which is why I can signal turns) and by the point the vehicle is alongside, the immediate danger of collision has usually passed anyway.
Of course, when it's been a really bad close pass, I've not thrown my hand up because I've been too busy diving into the verge! Twice this year so far, same bit of road. I'm sure several people will be delighted to know that groups I'm in now generally ride two abreast through it, with the outer one near the white line, and it's reduced offending.