The dotted-line face emoji (a face outlined in dots, with no solid features) signals invisibility, fading away, dissociation, or 'I'm not here' / 'I want to disappear'. Often used in jokes about social anxiety, exhaustion, or wanting to vanish from an awkward situation. If your teen sends it, they are joking about wanting to be invisible — usually playful, occasionally a softer way of expressing real overwhelm.