Basically all of the things I see other drivers doing when I'm not in their car.

• Distracted driving (e.g. phone)
• Resigning right-of-way in situations that are unsafe, like on highway entrance ramps and inside traffic circles
• Doing unpredictable things (e.g. quickly weaving through traffic, merging/turning without signaling)
• Zero clue about safe stopping distance for their vehicle, weight, and speed
• Cutting off freight, especially at highway speeds
• Generally unaware of what others are doing around them, only to wind up upset with others, then driving angry/aggressive
• Driving fast enough to overwhelm the car's suspension and traction (wheels leave ground, springs bottom out)

The last one is particularly nauseating and terrifying if you're in the car.