Final answer:
An excess of yellow bile, as per Galen's theory, would make a person exhibit a choleric temperament, which includes being irritable or aggressive. This aligns with being thoughtlessly rude and cold.
Step-by-step explanation:
According to Galen, a prominent Greek physician and philosopher, an excess of yellow bile would cause a person to exhibit a choleric temperament. The choleric temperament is characterized by being passionate, ambitious, and bold. Therefore, an excess of yellow bile would most likely lead to behavior that is confident and assertive, but can veer into being easily provoked or prone to anger. In the context of the question, the closest match would be that a person would be thoughtlessly rude and cold, reflecting a tendency to be irritable or aggressive due to an imbalance in the choleric humor.