flatFlat usually refers to dull and emotionless.
lacking interest or emotion; dull and lifeless; lacking vitality or animation.
It is often misused, I had to look for a while to find a good example, and this was the best I could do (it's not even a good sentence!)
Maybe because his flat eyes had no expression and he was squinting at me like a mob character.
Flat can similarly refer to affect, scenario, food or joke.
