Scenario 1; You're on a bus, its not even 1/3 full. The bus pulls into a stop and somebody gets on. Despite oodles of free double seats this person decides to take the one next to you.
Scenario 2; You're at the cinema, you're waiting to see Good Night & Good Luck. Accordingly the theatre is practically empty. As the trailers start a stranger makes his way in and proceeds to sit in the seat directly in front of you or 1 or two seats to the side.
Scenario 3; You're in the library, studying for your exams. Gerrymandering George takes the seat next to you and proceeds to redraw the border between desks by taking* a proportion of yours.
Is there anything more annoying? It's happening everywhere.
That is all.
* Edit typo