I think that is the attraction (or lack of it :) ) when you see a "x" as a Sim walks past another. You may also see hearts too when they are attracted?
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Townies sometimes kick the trash can if they have walked past the lot and the family have not interacted with them. I am unsure of the number of times the Townie walks past before this happens. Correct me if I am wrong but I think playable neighbours don't kick the trash can without good cause.
This pic shows Alexander Goth furious thought bubble with Nina Caliente for cheating with Don whilst Don is engaged to his sister, Cassandra.
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