The slight smile with closed, upturned eyes (often called the 'relaxed smile' emoji) signals quiet contentment, gentle warmth, or — for Gen Z — passive-aggression. Among older speakers it usually means 'I'm peacefully happy'. Among younger speakers it has acquired a sarcastic, slightly menacing tone, as in 'thanks so much ☺️' meaning the opposite. The difference is generational rather than malicious. If your teen sends it, it is more likely warmth than threat; if you receive one from a Gen Z colleague over a small mistake, be aware of the second reading. Tone of the message decides.