Some of my favorites are the guys that drop their bags in the first open bin and walk to the back of the plane so they don't have to carry it so far. When the space is finally needed by someone that actually sits there, I'm tempted to pull the offending piece out and tell the FA there's no room for it and don't know who left it there on the floor.

I saw one lady with a weeks worth of shopping boot someone out of "her" seat and cram the stuff everywhere. A late arriving passenger somehow had the same seat assignment as "her" seat. It was quickly discovered that she didn't know where her seat was. It was sure convenient that "her" seat was at the door with unlimited legroom.

Mostly I'm just happy to arrive alive.