right click and drag to delete notes
right click only -> show context menu (after button release)
right click and drag -> delete whatever gets hit
Personally, I'd prefer to activate an "eraser" mode. When activated, dragging over any notes deletes them. Maybe this "eraser" mode would be enabled by clicking an eraser icon or with a hotkey. Even something like holding CTRL while dragging over a note would be better than right clicking IMHO.