A friend and I had an interesting encounter. We're flying SEA-AMS-FRA, right two seats, center bulkhead, 747. I'm DL Plat, so we were among the first to board after F/J. We each had a small rollaboard and a small personal bag. I put one set of bags in the overheads above our center bulkhead, and then put the other set in the overhead across the aisle (seats A-B). Two couples board a bit later than us, sitting in the first two rows, A/B. One of the men proceeds to start reading me the riot act - I mean raised voice, looking around at other pax, trying to draw everyone in - because we had put bags in 'their' overhead bins. He and the others kept bleating about how experienced they were. He was very large - my friend and I are very small - and he was really working it. The FA finally calmed him down, and as he took his seat, he looked at his wife and back at the other couple and loudly declared "Some people are so rude. We're very well traveled and we know the rules. Next time, we're just going to fly first class".
The best part? This was Christmas/New Year's, so there was the slimmest of chances that we would have all ended up on the same flight home. I wish we had, because as we were boarding to come home, my friend and I both got upgraded to F.
I've witnessed this before - pax thinking the compartment above their seat is reserved for only their use. That's particularly problematic on some of the little RJs that have tiny bins on one side and roomier bins on the other. Those little bins are so small that I've had to readjust a small rucksack (personal item) to make it fit.