I used to work with this girl called Erin... well, I didn't work with her. She worked in a different team on my floor, but had to walk past my team any time she went anywhere. Erin is Canadian, and the sort of chirpy that leads your typical Brit to suspicious sideways glances and comments like "what's she taken?" Every morning, Erin would come in and say "Good morning!" and most of the people in my team would look up and go "...the fuck is up with her?"
The worst part was that she wasn't stupid. She was good at her job and clearly had a grasp on current affairs and the state of the world. You couldn't write her chirpiness off as her being a bit daft and not understanding how awful everything was.