As someone who always feels a bit self concious if I think I'm holding up a queue or somesuch I'm always amazed at how some people will wait until all their groceries have been scanned through before starting to pack them; will get on a bus and then calmly root through their bag and pockets for change or their travel card; will spend ages at the ATM putting in one card after another, scrutinising receipts etc while loads of people wait behind them.
AIBU to wonder how these people aren't sometimes mortified at the delays they're causing, the people looking at them and mentally throwing their eyes up to heaven etc?