I've seen people put very small handbags or man bags under Row 1 seats, but they are so small my feet wouldn't even reach them! But a full sized carry on - that is a joke!

I'd have removed it anyhow and reported it as being left and not engaged the actual passenger, just let Cabin Crew deal with it.

More generally, the issue of Locker Space around Row 1 can be annoying, especially when already being used by Cabin Crew, or marked as not for stowage. Not sure what the long term answer is however, as you have to put everything Up on Row 1 so can be awkward on some occasions.