If "smiling warmly" conveys friendliness and affection:
* Frowning coldly: This emphasizes a lack of warmth and perhaps even hostility.
* Staring blankly: This conveys indifference and a lack of engagement.
* Scowling angrily: This expresses negative emotions like anger or displeasure.
* Looking away dismissively: This suggests a lack of interest and a desire to distance oneself.
If "smiling warmly" suggests comfort and reassurance:
* Looking worried: This conveys anxiety and distress, the opposite of calming reassurance.
* Looking tense: This shows physical and emotional tension, the opposite of a relaxed and comfortable demeanor.
* Grimacing painfully: This suggests discomfort and pain, the opposite of a pleasant and reassuring smile.
Ultimately, the opposite of "smiling warmly" depends on the specific meaning you want to convey.