Guild Wars 2

I sometimes accidentally target something I don’t want – and I’m not talking about just clicking on a mob/player/npc, I mean when there’s a bright, distracting red target on them. Esc doesn’t deselect, and neither does clicking on the screen anywhere. How do I undo this? >-<

that is the target marker.
by default you set it by Ctrl+T on your current target

You can’t remove it unless the subject either dies or leaves render distance. you can however move it out of the way, by selecting something else and setting the target on it.