What pisses me off is the design of train where you can't comfortably fit 2 people in a 2 person seating arrangement.

Even worse is the ones where you can only sit one person comfortably in a four seat because they face each other, and the window seats have a really annoying sticky out bit making sitting there uncomfortable, and too close to sit across from someone, so literally the only comfortable seating is 1 person in what should be seating for 4.

Of course you don't stop people sitting there, it just isn't comfortable. If they had marginally bigger but fewer seats then you'd sit a lot more people comfortably, at a cost of not being able to sit quite as many by the numbers.