I was once behind someone who actually accelerated way faster to beat a yellow light than they did to merge onto the highway.
I sometimes get stuck behind an old fart who follows the imaginary variable speed limit signs in his or her head. Posted 45 means going 50, then 25, then 38, then back to 25, then to 40. Anything except 45. Not because of curves or road hazards or anticipation of turning off or anything really. Just random roadtardery.