When I boarded my US A321 flight from LAX to PHL, in 3F, I was in the middle of the F pack. There was already someone seated in 3D when I arrived. I put my carryon up top, and proceeded to my seat with my laptop bag. I look down, and my seatmate had already placed his jacket and laptop bag flat under the space in between the two seats in front of us.

Now, it’s really not a big deal to me as I sometimes prefer to lay my bag down, and rest my socked feet on it, but I’ve never had someone do that before. I’ve only had the opposite happen in the past, they usually wait for me to sit down, offer the space for my bag, I tell them, "Oh no, go ahead," and he places bag his in the space. Even if I didn’t want my bag at my feet, I would never assume the space, and take it all to myself.

Just wondering what others have experienced on this. Is it a first come-first served thing?