Learn English – A word for someone plays on your insecurities

An excellent word is malefactor, which is basically Latin for wrongdoer. And much like a benefactor acts benevolently to others, often anonymously or indirectly, the same is generally true for a malefactor acting malevolently - like in your Colonel's scheming*.

A phrase that frequently comes up in describing these characters is bad actor.

*See also the most famous malefactor of all time, Shakespeare's Iago.

While it's not specific to ending a conversation, consider pleasantries:

An inconsequential remark made as part of a polite conversation