On a flight to Cancun with my buddy, someone came to his bin space and took out his bag and replaced it with hers. She tried to put it in another bin, but it didn't fit and she left it in the aisle. We didn't realize this until he saw his bag in the aisle.
When my buddy asked why she did this, she said "because her seat was close".
"Do you know who I am, my seat is near yours and therefore I am entitled to pre-filled bin space"
The FA offered to take her bag out, but my buddy didn't want to delay the flight and accepted putting his bag back about 5 rows behind us.
The best part is the lady was non apologetic the whole time - in fact, she had a bit of an attitude when asked why she did this.