[marcusbooster]

Someone who "became visibly upset and arrogantly pointed his finger in the agent's face when asked why he did not have an airline ticket for a return flight." is different than someone who expresses discontent in a non-threatening manner.

The anecdote described by the agent about finger-waving is not in the guidelines. The actual guideline is very loose and will be interpreted by screeners as they see fit and as they see convenient. And they could use it in both situations you described.