My pet peeve, at least here where I live, are all the people that put little reflective things close to the road; those damned fenceposts with the reflective white tops, markers on their mailbox, markers to show them where their driveway is, etc., you name it. It seems people who live next to the road are like magpies and like to hoard and display shiny things.
I'm always looking for eyes at night and even though I ride the same road every night, it seems like every trip I get a small adrenaline rush when I'm examining something shiny down the road and trying to figure out if it's a reflective object or the eyes of an animal.
As noted, those dark green metal fenceposts with the reflective white tops are the worst. If you're in a rough spot and your headlight is bouncing around, they seem like they're flickering.
I have the luxury of being able to putt along at about 45 on the way home with no cars coming up behind me, so that's what I do. Takes longer to get home but, hey, it increases my riding time!