Does this fall under "irony" or "poetic justice?"

Well, whatever the case, this man's fate definitely falls under the heading of "stupidity:"

In this vein, we note with a sense of both sadness and irony a couple of articles recently called to our attention. The first is a 17 September 2004 editorial published in the Daily Nebraskan and entitled "Individual Rights Buckle Under Seat Belt Laws," by Derek Kieper, a 21-year-old senior at the University of Nebraska-Lincoln, in which the writer inveighed against mandatory seat belt laws, opining that "Uncle Sam is not here to regulate every facet of life no matter the consequences," and that "Democrats and Republicans alike should stand together to stop these laws that are incongruous with the ideals of both parties." In the midst of his editorial he noted:

As laws become increasingly strict for seat belts, fewer people will respond positively by buckling up in response to the laws. There seems to be a die-hard group of non-wearers out there who simply do not wish to buckle up no matter what the government does. I belong to this group.

Evidently his words were far more prescient than any of us might have wanted, as an article in the 4 January 2005 Lincoln Journal Star reported that Mr. Kieper not only died in a car crash, but the tragic mishap that claimed his life was the very type of accident in which seat belts have proved so effective in saving lives — preventing passengers from being ejected from vehicles

It's always sad and tragic when people die like that, but you have to admit the guy was just asking for it.