Typical folks cutting in front of me while I am barely at safe breaking distance from the car in front of me, on speeds > 100kmh. This is of course always in at least semi-dense traffic, and them immediately obscuring view further means I have less than second to react to any stronger breaking or I slam into them.

I honk them, then they often get aggressive that I dared to react to their perfectly cool maneuver that gave them those precious extra 5 seconds. Bloody a-holes. Had few almost-collisions even this year due to too aggressive drivers riding too close, some were literally car in front of us or next one behind. Keep your distance, I can't emphasize this enough.

My hand gesture for "Hey did you hear about the inverse Pascal Scam? It suggests that low-probability high-impact risks are easy to ignore, and I think that's what you're doing right now and that's not going to be good for your health, or mine for that matter, so maybe think about that a bit more in the future" is to raise my middle finger. Unfortunately it inevitably makes the situation worse somehow.