I once saw someone had a MASSIVE backpack. Like; triple strap hip, belly, and chest strap backpack; probably 15kg (33lb) or something. I think it just barely technically was allowed when they were weighed. They were struggling to carry it.

Then I realised they were a small group, and all sitting on the same row, and all 4 of them had one of these backpacks. They took up two entire overhead carriages by themselves. Other people had to put their luggage and belongings in random places around the plane where there was space. Everyone was in a flurry to try and stay on schedule, it held up the whole plane lol