On a merging lane of a 100 Km/h highway, an old woman in front of me decided that to merge safely, you must NOT at any cost match the speed of traffic then look for a hole to insert yourself, but instead come to a complete stop and keep looking in your mirrors until you can see no car coming so that you have then to merge into the highway from a stop. Luckily for her, there was enough space on the shoulder to pass her car or I and others would probably have slammed in her rear.
As a honorary mention, I'd like to mention the typical guy in a truck swerving in pretty dense traffic at 70-80 Km/h to save a few seconds off of their travel time. The guy in question this time misjudged the size of his truck and the space available to him and rammed into the front bumper of a Dodge Grand Caravan, disintegrating the front panels on the side he hit and tearing off the front bumper. I can still see the pieces in the air after the collision. The guy in the truck didn't stop, he just sped away and kept swerving in and out of lanes. I didn't stick around to see what happened to the Caravan, as the safest thing to do was to continue at the same speed. It wasn't particularly "suicidal" but it was goddamn stupid and he gets bonus points for actually causing an accident.
There was also those kids in a truck in stop-and-go traffic on two lanes (the one where you're stopped 1 minute, then you can move at 30 Km/h for 10 seconds then you're stopped another minute), where, seeing that the car in front of them didn't fill the space in front of it fast enough to their taste, they accelerated with wide-open throttles to make a dangerous maneuver where they changed lane in front of someone in the right lane, forcing them to brake hard, then changed again to the left lane to get to the space that was in front of the car that was previously in front of them and they absolutely wanted to get it and shave 2 seconds off their trip. Worse than that, they had the gall to honk at the car in front for not speeding up and closing the space fast enough even if there was no chance of it being taken by anyone and getting there fast would make no difference. Again, not suicidal due to the slow speeds involved, but just maddeningly stupid.