We'll call him Bozo.
I'm sitting happily up front on a packed flight, wondering if the pax in the window seat next to me is going to make it. With minutes to spare, he comes bustling into the cabin, slamming the bins, storing his carry on and officiously directing his female companion to the seat behind him. He is big, loud and brash, dressed in flipflops, shorts and a Polo shirt that is inside out. I get up and he blunders to his seat, dropping on top of his pillow and blanket. There is a loud pop as the plastic enclosing the blanket bursts. He sat on top of them the whole flight.
I thought about offering to change seats with the companion, but didn't want to give up my aisle seat or sit behind someone who would surely ratchet his seat all the way back for the entire flight. Poor decision.
Bozo doesn't bother to turn to speak to his companion; rather, he faces forward and raises his voice. The whole cabin hears about his Learjet. Right. He powers up his laptop as the boarding door closes and spends several minutes banging away, then snaps it shut, shoves it carelessly partway into the seatback pocket and never secures the tray table, so it hangs halfway open. This arrangement remains in effect during taxi and takeoff. At no point in the flight does he ever fasten his seatbelt. The FAs fail to notice any of this.
Bozo can't be still. He is constantly moving, fidgeting, changing position. A great deal of the fidgeting involves rearranging his, um, equipment. He slows down while watching the movie, then resumes the fidgeting. Finally he shoves his hand down his shorts

and drifts off to sleep, but is awakened almost immediately by the arrival of the snack basket. He eats his cookie with *that* hand. Bleah.
Landing is rough and bouncy. Bozo isn't bucked, of course, so he clutches the armrests and lets out a little yip of terror. I smile.
I flee the plane, reflecting that the quality of my future seatmates can only go up.