Cancel buttons in lifts.
I keep pushing the wrong floor button and then as soon as I've realised I've done it there's nothing I can do but wait for the damn thing to make an extra stop on the wrong floor. I fill like a bit of a dick standing on my own, in the middle of a lift, watching the doors open on a floor I don't intend to get out on, staring at the people working on that floor staring at me as the doors open, standing and waiting as the doors close, still staring at the people staring at me.

It's an awkwardness they could be avoided if they had cancel buttons.