One of my biggest pet peeves are if I see luggage turned sideways in a standard sized bin. Think domestic or southwest flights with 3x3 configs. 21 in. carry ons are designed to fit straight into those bins, but people always seem to put it in sideways. This is even worse when people put in smaller carry-ons, or laptop bags in sideways and does not maximize the bin space.

Similarly, I've noticed more and more people bringing on 22 in. or even large carry ons that will not fit straight in. Shouldn't gate agents be experts on estimating the size of the luggage since they see hundreds of them every day now? Like how casino pit bosses can eye the chip tray in seconds and know how much is in it.